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Article

Construction of Cu2O-ZnO/Cellulose Composites for Enhancing the Photocatalytic Performance

by
Yuchen Li
,
Ming Yan
*,
Xin Li
and
Jinxia Ma
*
Jiangsu Co-Innovation Center of Efficient Processing and Utilization of Forest Resources, Jiangsu Provincial Key Lab of Pulp and Paper Science and Technology, College of Light Industry and Food, National Engineering Research Center of Biomaterials, Jiangsu Engineering Research Center of Bamboo and Wood Carbon Fixation Materials and Structures, Nanjing Forestry University, Nanjing 210037, China
*
Authors to whom correspondence should be addressed.
Catalysts 2024, 14(8), 476; https://doi.org/10.3390/catal14080476
Submission received: 1 July 2024 / Revised: 11 July 2024 / Accepted: 18 July 2024 / Published: 25 July 2024
(This article belongs to the Section Photocatalysis)
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Abstract

Zinc oxide (ZnO) nanoparticles, as a non-toxic, harmless, and low-cost photocatalytic material, have attracted much attention from the scientific and industrial communities. However, due to their small particle size and high surface energy, ZnO nanoparticles are prone to agglomeration. In addition, ZnO nanoparticles only have catalytic activity and electron–hole pairing under ultraviolet light. Therefore, Copper(I) oxide (Cu2O)-ZnO/cellulose composites with excellent photocatalytic performance were fabricated by loading Cu2O crystals and using cellulose fiber substrate in this work. Cu2O can increase the light absorption range (including ultraviolet light and visible light) of ZnO/cellulose composites. Moreover, Cellulose fibers can improve the contact area to pollution and photostability of the Cu2O/ZnO nanoparticles, thereby enhancing the photocatalytic activity. The Cu2O-ZnO/cellulose composite showed the highest photocatalytic activity for Methyl orange (MO) degradation, which was approximately 40% and 10% times higher than those of the ZnO/cellulose and Cu2O/ZnO composites, respectively. Moreover, the degradation rate of phenol reached 100% within 80 min. The highly enhanced activity of the Cu2O-ZnO/cellulose composite is attributed to the enlargement of the light absorption range and the formation of heterojunctions between the counterparts, which effectively suppress the recombination of the photogenerated charge carriers. Overall, this work aims to improve the photocatalytic activities of ZnO/cellulose composites by loading Cu2O crystals, hoping to provide a novel and efficient photocatalyst for wastewater treatment.

1. Introduction

Recently, water pollution has become a serious threat to human beings due to the increasing content of organic matter. Thus far, the treatment for removing organic matter in water includes chemical precipitation, ozone oxidation, hypochlorite oxidation, electrochemical methods, and adsorption [1,2]. However, these methods have the disadvantages of poor selectivity, low efficiency, and high cost. Semiconductor materials can produce electron–hole pairs excited by light energy, which is conducive to detoxicating organic pollutants or splitting water into hydrogen [3,4]. Therefore, various semiconductor materials have been successfully applied in the treatment of water pollution. Zinc oxide (ZnO), with a wide band gap energy (3.37 eV) in the near ultraviolet spectral region, has received increasing attention because of its low cost and high photocatalytic performance [5,6,7]. However, ZnO nanoparticles, like most powder catalysts, have some obvious drawbacks in the application of photocatalytic degradation. On the one hand, ZnO nanoparticles are easy to agglomerate due to the small particle size and large surface energy, which will lead to inefficient contact with reactants in the photocatalytic process. Moreover, the small particle size of ZnO nanoparticles may make the recovery and reuse difficult, thus easily causing secondary pollution. On the other hand, the adsorption capacity of ZnO nanoparticles to pollutants is weak, which may limit the photocatalytic efficiency. To alleviate the agglomeration encountered in the photocatalytic application of ZnO nanoparticles, various substrates such as chitosan, starch, or cellulose have been developed to disperse and fix them [8]. They can effectively increase the contact area with pollutants, enhance the photocatalytic performance, and improve the recycling capacity of ZnO photocatalysts.
Cellulose, as the most abundant natural polymer on earth, has advantages such as low cost, renewability, degradability, and rich surface groups [9,10]. It is significant that the OH group on the cellulose fiber surface can firmly combine with ZnO due to the electrostatic attraction, thus effectively reducing the agglomeration and improving the photocatalytic activity of ZnO photocatalysts [11]. Unfortunately, there are still some limitations of ZnO/cellulose composite photocatalysts in practical applications. Due to the wide band gap of ZnO, ZnO/cellulose composites can only absorb 5% of sunlight and they are only active under UV light [12]. Furthermore, the rapid recombination rate of photogenerated electron–hole pairs will weaken the photocatalytic performance of ZnO/cellulose composites. Therefore, many researchers have sought to prevent the recombination of ZnO electron–hole pairs to improve photocatalytic activity through various strategies, such as surface modification and doping [13]. It is known that the doping strategy can significantly improve the photocatalytic efficiency of ZnO under visible light by coupling narrow bandgap semiconductors [14]. The common doping strategies include ion doping, noble metal doping, and metal oxide modification, which aim to improve the photocatalytic activity of ZnO by changing the energy band structure, creating effective photocatalytic reaction sites, and increasing the mobility of charge carriers [13]. Our group reported an Al doping in the ZnO/cellulose composite method to inhibit the recombination of photogenerated electron–hole pairs, and the corresponding results showed that the photocatalytic performance of Al-ZnO/cellulose composite under UV light was greatly improved [15]. However, the poor photocatalytic activity of ZnO/cellulose composite under sunlight has still not been well addressed. Huang et al. employed nanocrystalline cellulose (NCC) as a template to synthesize Ag-doped ZnO nanoparticles via an in situ precipitation method and heat treatment [16]. Compared with ZnO/NCC composite, Ag doping can effectively extend absorption in the visible light region, thus promoting the generation of electron–hole pairs and prolonging their lifetime. Within 120 min under visible light, the photocatalytic degradation rate of the Ag-ZnO/NCC composite can reach 99.2%, which is higher than the ZnO/NCC composite (88.0%). Unfortunately, this method of preparing Ag-ZnO/NCC composites is cumbersome and costly, which is not suitable for practical application. Therefore, it is necessary to find an alternative material with a simple preparation process and high light utilization efficiency to improve the photocatalytic activity of ZnO/cellulose composites.
Cu2O is considered a P-type semiconductor with narrow band gap energy ranging from 2.0 to 2.2 eV, which could effectively utilize a large amount of visible light [17]. Therefore, Cu2O-based photocatalysts have been widely applied in the application of organic-pollutant decontaminations [18]. However, there are still many constraints on its application, such as the instability in oxidizing conditions, the rapid recombination of photogenerated holes and electrons, and the crystalline structure transformation during the reaction. Interestingly, the deposition of Cu2O with a narrow band gap of Cu2O on ZnO/cellulose composites can endow a wide band gap of ZnO. Therefore, coupling Cu2O with ZnO can not only increase the absorption of visible light, but the heterojunction of ZnO/Cu2O composites could also promote the separation of the photo-generated electron [19], thus improving the photocatalytic performance. However, the relevant research regarding the surface modification of ZnO/cellulose composites with Cu2O to improve photocatalytic activity is relatively scarce.
In this work, UV-vis light-driven Cu2O-ZnO/cellulose composite photocatalysts have been successfully prepared via a simple chemical precipitation method. The corresponding results illustrated that Cu2O loaded on ZnO/cellulose composites could not only change the morphology of ZnO but also showed a wider light absorption range and higher electron separation efficiency. Moreover, the phase structure, morphology, optical properties, and stability of the prepared composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform-infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (UV-vis DRS), and photoluminescence spectroscopy (PL) techniques, respectively. The photocatalytic activity of Cu2O-ZnO/cellulose composites was based on the catalytic degradation of model pollutants (methyl orange, MO) under UV-vis light. The results showed that the as-prepared products possessed significant photocatalytic performance and could be recycled without obvious decay. Overall, this work aims to combine common photocatalysts with biodegradable materials to provide an efficient and green biomaterial nano-photocatalyst for environmental remediation.

2. Results and Discussion

2.1. The Morphology and Microstructure of Cu2O-ZnO/Cellulose Composite

The microstructure and morphology of the Cu2O-ZnO/cellulose composite are shown in Figure 1. It can be found that flower-like ZnO particles, composed of many sheets, have been successfully fixed on the cellulose fiber surface. The average diameter and thickness of the flower-like ZnO particles can reach approximately 1 μm and 20 nm, respectively. Furthermore, there are many spherical particles with diameters of ~100 nm homogeneously distributed on the ZnO surface. It can be found from Figure 1d–f that the Cu, Zn, O, and C elements are uniformly dispersed on the Cu2O-ZnO/cellulose composite. The contents of Cu, Zn, O, and C are 11.2, 49.5, 11.9, and 27.4 wt%, respectively. Therefore, it can be concluded that the spherical particles homogeneously distributed on the ZnO surface are Cu2O particles. Moreover, it can be found from Figure 1b that there are no spherical particles on the surface of the ZnO/cellulose composite, which further confirms the successful loading of Cu2O particles on the Cu2O-ZnO/cellulose composite (Figure 1a). Compared with the Cu2O-ZnO/cellulose composite, more and bigger Cu2O particles are accumulated on the Cu2O/ZnO powder surface (Figure 1c), which demonstrates a significant reduction in the number of Cu2O particles distributed on the Cu2O-ZnO/cellulose surface.
This phenomenon can be attributed to the steric hindrance effect by cellulose fibers, thus resulting in a more uniform dispersion of Cu2O on the ZnO/cellulose surface. Consequently, the Cu2O-ZnO/cellulose composite without any agglomeration or accumulation of Cu2O particles can provide a larger contact area with pollutants. Overall, the results indicate that cellulose fibers as the substrate can play a role in fixing and dispersing nanoparticles, which can prevent their agglomeration and enhance their photocatalytic activities.
To further investigate the interactions between cellulose and Cu2O-ZnO, the Cu2O-ZnO/cellulose composite, the ZnO/cellulose composite, and Cu2O/ZnO powder have been analyzed by XRD, FTIR, and XPS methods. It can be found from Figure 2a that the Cu2O-ZnO/cellulose composite and the ZnO/cellulose composite possess the typical diffraction peaks at 2θ = 14.71, 16.64°, and 22.33°, which are ascribed to the (101), (10 1 ¯ ), and (002) planes of cellulose. Moreover, the characteristic peaks at 31.8°, 34.5°, 36.2°, 47.8°, 56.5°, 62.8°, and 68.0° all existed in the XRD diagram of the ZnO/cellulose composite, Cu2O/ZnO powder, and Cu2O-ZnO cellulose composites, which correspond to (100), (002), (101), (102), (110), (103), and (112) crystal planes of ZnO wurtzite, respectively [20]. This phenomenon indicates that the presence of Cu2O can not affect the ZnO crystals [21]. It can be observed that the Cu2O-ZnO/cellulose composite and Cu2O/ZnO powder both possess characteristic peaks at 2θ = 29.6°, 43.3°, 61.4°, and 73.8°, which corresponded to the peaks of the Cu2O crystal the peaks of (100), (111), (200), (220), and (311) [22]. These results demonstrate that the Cu2O and ZnO are successfully loaded onto the Cu2O–ZnO/cellulose composites. FT-IR analysis has been employed to investigate the surface functional groups of all samples (Figure 2b). The peak of 610 cm−1 is the stretching vibration of the Cu-O bond and the peak at 1315 cm−1 is the symmetrical bending vibration of the CH2 and COH groups. In addition, the peaks at 1059 cm−1 and 1024 cm−1 are caused by the -CH2OH stretching and -CH2 bending vibrations, respectively. Compared with cellulose, it can be found from the ZnO/cellulose compositethat the signal near 1059 cm−1 redshifted and the signal near to the 3310 cm−1 region moved relatively close to the low band. This phenomenon indicates that there is a strong interaction between ZnO and the hydroxyl of cellulose [22]. Compared with the ZnO/cellulose composite, there is a Cu-Zn-O stretching vibration at 1120 cm−1 for the Cu2O-ZnO/cellulose composite, which further proves the bonding effect between ZnO and Cu2O [23].
Structural information on the samples has been obtained by using the XPS analysis. It can be found that Zn and Cu2O are successfully introduced into the Cu2O–ZnO/cellulose composite (Figure 2c), which corresponds to the results of SEM and FT-IR. Figure 2d shows the high-resolution spectra of Zn 2p in the Cu2O–ZnO/cellulose composite, Cu2O/ZnO powder, and ZnO/cellulose composite. The peaks at 1021.0 eV and 1044.1 eV correspond to Zn 2p3/2 and Zn 2p1/2, respectively. It can be observed that the binding energy of Zn 2p of the Cu2O–ZnO/cellulose composite is 23.1 eV, which is consistent with the ZnO/cellulose or pure ZnO nanoparticles [24]. It proves that the Zn elements in Cu2O-ZnO/cellulose composites are normally present in the form of ZnO. Notably, the binding energy of Zn 2p in the Cu2O-ZnO/cellulose composite is transferred to a lower position compared to the ZnO/cellulose composite. It is well known that binding energy shifts in XPS spectra are attributed to two different reasons: the different electronegativities of metal ions and the strong interaction (of the electron transfer) ring between nanocrystals [25]. Therefore, it can be drawn that the transfer of binding energy for the Cu2O-ZnO/cellulose composite is because of the interaction between the Cu2O crystal and ZnO [26]. Moreover, it further proves that the interaction between ZnO and Cu2O can successfully modify Cu2O on the ZnO surface, thus endowing it with higher photocatalytic activity. Figure 2e shows the O1s spectra of the Cu2O–ZnO/cellulose composite, the Cu2O/ZnO powder, the ZnO/cellulose composite, and the cellulose. The peaks at 531.4 eV and 529 eV are assigned to the Cu2O lattice and ZnO lattice, respectively [20]. Figure 2f exhibits the high-resolution Cu2p spectra of all samples. The Cu2O-ZnO/cellulose composite and Cu2O/ZnO powder have two obvious peaks at 934.0 and 953.3 eV, which correspond to Cu2p3/2 and Cu2p1/2, respectively. It illustrates that the copper in the sample mainly exists in the form of univalent Cu+ [27], proving the existence of Cu2O in the Cu2O-ZnO/cellulose composite and Cu2O/ZnO powder.

2.2. Photocatalytic Activity of Cu2O-ZnO/Cellulose Composite

To explore the potential application of the as-synthesized Cu2O-ZnO/cellulose composite in wastewater treatment, MO degradation has been investigated under UV-vis light irradiation by employing the Cu2O-ZnO/cellulose composite as the photocatalyst. As shown in Figure 3a, the Cu2O-ZnO/cellulose composite, the ZnO/cellulose composite, and the Cu2O/ZnO powder all reach the adsorption equilibrium within 40 min in the dark condition. It can be found that the Cu2O/ZnO powder has lower adsorption performance than the ZnO/cellulose composite and the Cu2O-ZnO/cellulose composite. Figure 3b shows that MO macromolecules cannot be photodegraded without photocatalysts. In contrast, the Cu2O-ZnO/cellulose composite can photodegrade 96% MO within 80 min. However, the photocatalytic activity of the ZnO/cellulose composite has only a 54.8% degradation rate within 80 min, which is far below that of the Cu2O-ZnO/cellulose composite. It proves that Cu2O can play a positive role in the surface modification of the ZnO/cellulose composites, thus improving the light absorption range and photocatalytic performance. Moreover, the photocatalytic activity of the Cu2O/ZnO powder is 81.4% within 80 min, which is also lower than the Cu2O-ZnO/cellulose composite. The porous network structure of cellulose also plays a key role in the fixation and dispersion of Cu2O/ZnO particles, thus avoiding the agglomeration of Cu2O/ZnO particles, which is consistent with the results of SEM. Therefore, the Cu2O-ZnO/cellulose composite can efficiently utilize light energy and maximize its photocatalytic performance. The corresponding linear relationship between −ln(C/C0) and irradiation time t is shown in Figure 3c. It can be found that the photocatalytic degradation reactions of all samples conform to the pseudo-first-order kinetics rules. The photocatalytic degradation rate constant of the Cu2O-ZnO/cellulose composite is 0.0325 min−1, which is much faster than the ZnO/cellulose composite (0.0093 min−1) and the Cu2O/ZnO powder (0.0194 min−1). Overall, it can be concluded that the dispersion and fixation of Cu2O and ZnO on the cellulose fiber can improve the photocatalytic activity of the Cu2O-ZnO/cellulose composite.
The photocatalytic degradation of phenol was investigated using UV-visible spectroscopy for the Cu2O-ZnO/cellulose composite, the Cu2O/ZnO powders, and the ZnO/cellulose composite. Figure 3d illustrates the change in phenol concentration over irradiation time. The control experiment demonstrates that phenol exhibits minimal degradation in the absence of a photocatalyst. All samples are agitated in darkness for 30 min to achieve adsorption equilibrium, and the impact of adsorption is evidenced by the declining trend in phenol concentration. The results indicate that the adsorption performance of the Cu2O-ZnO/cellulose composite surpasses that of the Cu2O/ZnO powder, a phenomenon closely associated with the presence of cellulose. Under UV-vis light, the Cu2O-ZnO/cellulose composite demonstrates superior photocatalytic performance, achieving the complete degradation of phenol under ultraviolet–visible light irradiation for 80 min. This underscores the significant synergistic enhancement for the photocatalytic effect of composites by Cu2O and ZnO, while also highlighting the role of cellulose fibers in enhancing the fixation and dispersion effects of Cu2O and ZnO, thus improving the photocatalytic action. Kinetic studies demonstrate that the degradation of phenol con-forms to quasi-first-order kinetics, as represented by the equation ln (Ct/C0) = k. k represents the apparent rate constant, Ct denotes the concentration of phenol in the reaction system at various irradiation times, and C0 stands for the initial concentration of phenol. By plotting the relationship between −ln (Ct/C0) and the irradiation time of the light source (Figure 3e), the rate constant k can be determined. The calculated rate constants for the ZnO/cellulose composite, the Cu2O/ZnO powder, and the Cu2O-ZnO/cellulose composite are 0.01 min−1, 0.0394 min−1, and 0.0625 min−1, respectively. The Cu2O-ZnO/cellulose composite has the highest efficiency in degrading phenol, with a rate constant that is 6.25 times that of the ZnO/cellulose composite.
Table 1 presents a comparison of the reaction rate constants for degrading simulated organic pollutants in the prepared Cu2O-ZnO/cellulose composite with those reported in similar studies conducted domestically and internationally. The catalyst utilized in this investigation possesses distinct advantages. Nevertheless, these catalysts predominantly exist in powdered form, posing challenges to their recyclability and reusability, potentially leading to secondary water pollution.
To better explain the improvement of photocatalytic activity by Cu2O in the Cu2O-ZnO/cellulose composite, the separation behavior of the charge carrier has been investigated from photoluminescence spectroscopy (PL). It can be observed from Figure 3f that the Cu2O-ZnO/cellulose and ZnO/cellulose composites both have wide emission bands in the wavelength range of 350~650 nm. The highest emission peak first appears at 420 nm and then a small emission peak appears near 480 nm. Moreover, there is a small emission peak near 500 nm in all samples. Notably, the Cu2O-ZnO/cellulose composite possesses lower PL intensity than the ZnO/cellulose composite. It is known that the low spectral intensity of PL is beneficial to improve the efficiency of the photogenerated carrier separation of photocatalysts, thus contributing to improving photocatalytic activity [28]. Therefore, it can be deduced that Cu2O significantly promotes the separation of electron–hole pairs and greatly improves the efficiency of charge transfer of the Cu2O-ZnO/cellulose composite. Overall, it can be concluded that the coupling of Cu2O to the ZnO/cellulose composite endows it with high photocatalytic activity, which further proves the synergistic effect of Cu2O and ZnO in the enhancement of photocatalytic activity.
The UV-vis diffuse reflectance spectrum (DRS) has been measured to investigate the optical absorption capability of the Cu2O-ZnO/cellulose composite. It can be observed from Figure 4a that the absorption of the Cu2O-ZnO/cellulose composite has a slight redshift compared with Cu2O/ZnO powder. This phenomenon might be due to the fixation and dispersion of cellulose fibers for a more uniform distribution of Cu2O/ZnO particles on the cellulose fiber surface, which is consistent with the SEM result. Compared with the ZnO/cellulose composite, the Cu2O-ZnO/cellulose composite and Cu2O/ZnO powder both have a visible light absorption capacity in the range of 400–800 nm. This indicates that Cu2O can improve the light absorption range, thus promoting the absorption efficiency of visible light of the Cu2O-ZnO/cellulose composite and Cu2O/ZnO powder [29]. Figure 4b depicts the band gap value of the Cu2O/ZnO powder, the Cu2O-ZnO/cellulose composite, and the ZnO/cellulose composite, which are 2.53, 2.54, and 3.14 eV, respectively. It can be found that the band gap value of the Cu2O-ZnO/cellulose composite is lower than the ZnO/cellulose composite, which illustrates that the energy requirement for the electron transition of the Cu2O-ZnO/cellulose composite is less than the ZnO/cellulose composite. This phenomenon indicates that the Cu2O-ZnO/cellulose composite is more easily excited by light to produce photogenerated electrons and holes, thus possessing a higher photocatalytic activity [30]. Moreover, the band gap value of the Cu2O/ZnO powder and the Cu2O-ZnO/cellulose composite is similar, which further proves that the cellulose fiber will not affect the light absorption capacity of the Cu2O-ZnO/cellulose composite.
To further explore the photocatalytic mechanism of the Cu2O-ZnO/cellulose composite, the main active substances in the photocatalysis process have been analyzed by adding different trapping agents. Tert Butanol (TB), Benzoquinone (BQ), and KI are used as the respective trapping agents of ·OH−, ·O2−, and h+ [31,32]. The effects of different trapping agents on photocatalysis are illustrated in Figure 4c. It can be observed that the photocatalytic degradation rate of MO in a Cu2O-ZnO/cellulose composite without a trapping agent can reach ~96% as it exposed to UV-vis irradiation for 80 min. However, the photocatalytic degradation rate of MO by adding TB, BQ, and KI trapping agents is only 30%, 26%, and 60%, respectively. Moreover, it can be found from Figure 4d that the photochemical degradation rate constant for the sample containing BQ, TB, and KI trapping agents is 0.0040, 0.0035, and 0.0093 min−1, respectively, which is consistent with the result of MO photocatalytic degradation rate. Therefore, it can be drawn that OH− and ·O2− are the main active substances for MO degradation in the photocatalysis process. Furthermore, the Cu2O-ZnO/cellulose composite can absorb photons to produce abundant electron–hole pairs under UV-visible light. It illustrates that h+ in the valence band plays an important role in the photocatalytic degradation of MO.
The photocatalytic mechanism of the Cu2O-ZnO/cellulose composite for the degradation of MO is shown in Figure 4e. The separation of holes/electrons in the Cu2O-ZnO/cellulose composite is thought to play a role in the production of ·OH radicals. It is well known that the ·O2− plays an important role in the decoloration of dye [33]. Under visible light irradiation, Cu2O can be excited according to Formula (1). Then, the generated electrons in Cu2O are immigrated to the conduction band (CB) of ZnO (Formula (2)) [34]. This transfer process is thermodynamically favorable because the CB of Cu2O lies above that of ZnO. Furthermore, this transfer process can promote the separation of e− and h+, thus reducing the recombination rate of photogenerated electron–hole pairs and extending the lifetime of hole pairs. Meanwhile, the generated electrons probably react with dissolved oxygen molecules and produce·O2−. The h+ can form ·OH with H2O through oxidation (Formulas (3) and (4)). Therefore, the MO dye can be oxidized to CO2 and H2O by the powerful oxidizing agent (OH and ·O2−), which is consistent with the photocatalytic mechanism in other works (Formulas (5) and (6)) [35].
According to the upper discussion, it can be concluded that the cellulose fiber can fix and disperse Cu2O and ZnO particles, thus improving the contact area with pollutants and facilitating photocatalytic efficiency. Furthermore, the coupling of Cu2O and ZnO particles successfully extends the absorption range to the visible light region, which promotes the electron–hole pair separation of the Cu2O-ZnO/cellulose composite, thus achieving higher photocatalytic activity.
Cu2O + hv → Cu2O (e−) + Cu2O (h+)
ZnO (e−) + O2 → ZnO + ·O2−
Cu2O (e−) + O2 → Cu2O + ·O2−
Cu2O (h+) + OH− → Cu2O + ·OH
Dye + ·O2− → products
Dye + ·OH → products
It is known that the catalysts serve as an accelerator to increase the catalyst reaction rate but without being consumed themselves. Therefore, the recyclability of photocatalysts is important in the practical application. The recyclability of the Cu2O-ZnO/cellulose composite has been investigated by the degradation of MO with identical conditions for five cycles under UV-vis irradiation. The Cu2O-ZnO/cellulose composite in each experiment is washed, filtered, and dried. It can be observed from Figure 5 that the cycle efficiency of MO by the Cu2O-ZnO/cellulose composite is still 90% after five cycles. This further proves that the fixation and dispersion of cellulose fiber can improve the stability and reusability of the Cu2O-ZnO/cellulose composite. The results suggest that the Cu-ZnO/cellulose composite possesses practical application potential as an effective and stable photocatalyst for the degradation of dyes under UV-vis irradiation. In addition, the recycling of the Cu-ZnO/cellulose composite can not only reduce the consumption of resources but also has important practical significance for the construction of an environmentally friendly society.

3. Experimental

3.1. Materials

Softwood bleached kraft pulp (SBKP) with a diameter of ~29.03 μm (aspect ratio of ~84.01 and cellulose content of ~95.85%) was provided by Suzhou Xinye Paper Co., Ltd. (Suzhou, China) Zinc chloride (ZnCl2), sodium hydroxide (NaOH), cupric chloride (CuCl2), hydrazine hydrate, and methyl orange dye (MO) were all provided by Nanjing Chemical Reagent Co., Ltd. (Nanjing, China). All chemicals were used without further purification.

3.2. Preparation of ZnO/Cellulose Composite

A total of 2.72 g ZnCl2 was dissolved in 100 mL of distilled water and then 2 g SKBP was added. The mixture was vigorously stirred for 2 h at room temperature. Then, 1 mol/L NaOH solution was added to the above reaction system to precipitate Zn2+ completely, in which the molar ratio of Zn2+ to OH− was 1:6 and the reaction time was 2 h under the same conditions. Subsequently, the products were washed three times with deionized water and filtered. The ZnO/cellulose composite was gained after the drying process (60 °C, 6 h).

3.3. Preparation of Cu2O-ZnO/Cellulose Composite

The CuCl2 was dissolved in 200 mL distilled water and mechanically stirred for 10 min at room temperature. The ZnO/cellulose composite was added to the system as the CuCl2 solution was uniform and transparent blue. Then, the mixed system was mechanically stirred for 2 h to ensure that Cu2+ was uniformly attached to the surface of ZnO/cellulose composites. The hydrazine dihydrate, as a reducing agent, was added to the above mixture dropwise until the mixture became dark orange and the reaction continued for 1 h at 70 °C, aiming to transform Cu2+ to Cu+ by the reduction reaction. Finally, the suspension was cooled to room temperature, and then washed with deionized water and ethanol more than three times. The Cu2O-ZnO/cellulose composite was dried at 60 °C in a vacuum drying oven. For comparison, the ZnO/cellulose composite was prepared according to the above methods, outlined in Section 2.2. Moreover, the Cu2O/ZnO powder was synthesized as a control sample without adding cellulose. Figure 6 shows the flowchart of the preparation process of the Cu2O-ZnO/cellulose composite.

3.4. Characterization of Samples

The morphology of Cu2O-ZnO/cellulose composites was characterized by field-emission scanning electron microscopy (FE-SEM, JSM7600 F, JEOL, Tokyo, Japan) with the accelerating voltage parameter of 15 kV. The X-ray powder diffraction (XRD) analysis was performed to investigate the crystal phase and purity of samples. The X-ray powder diffractometer (Ultima IV, Rigaku, Tokyo, Japan) was monochromatic Cu Kα radiation at λ = 1.540 56 Å in the 2θ range of 5~80° at a scan rate of 10 deg/min. The X-ray generator tension and current were 40 kV and 30 mA, respectively. A Fourier-transform infrared (FTIR) spectrometer (VERTEX 80V, Bruker Corp, Karlsruhe, Germany) was used to measure the chemical structure of the samples by using the potassium bromide (KBr) disk method. The wavenumber of FTIR was scanned at the range of 4000~400 cm−1. The optical properties of the products were characterized in the wavelength interval between 200 and 800 nm by using a solid-phase ultraviolet spectrometry (solid UV-vis) device (Lambda 950, PerkinElmer Corp., Shelton, CT, USA). The elemental analysis and the banding energy were studied by XPS (AXIS UltraDLD, Shimadzu, Tokyo, Japan). The photoluminescence (PL) spectra measurement was performed on a fluorescence spectrophotometer (LS55, PerkinElmer, Waltham, MA, USA) at room temperature by using a He-Cd laser line of 290 nm.

3.5. Photocatalytic Activity of Samples

A total of 0.3 g of Cu2O-ZnO/cellulose composite was added in 15 mL MO aqueous solution with a concentration of 6 mol/L or phenol (C6H5OH, 60 mg/L, 15 mL), followed by magnetically stirring in the absence of light for 30 min to reach the adsorption–desorption equilibrium before the photocatalytic reaction. Then, the MO or phenol solution with the Cu2O-ZnO/cellulose composite was exposed under a 6.6 W UV-vis lamp (CEL-HXUV300; Beijing Zhongjiao Jinyuan Technology Co., Ltd.; Beijing, China). A total of 1 mL liquid supernatant was taken out for testing at the selected time intervals and subsequently poured back into the reactor. The concentration variations of the mixture were determined by the UV-vis spectrophotometer (TU-1900; Suzhou Sainz Instrument Co., LTD., Suzhou, China) at maximum absorbance wavelengths of 465 nm of MO and 211 nm of phenol. Photodegradation efficiency (A) was calculated according to the following equation, A = C/C0 × 100%. In the equation, C represented the concentration of MO or phenol before UV-vis irradiation at the time. C0 was the concentration of MO and phenol at the selected irradiation time.

3.6. Reusability of Cu2O-ZnO/Cellulose Composites

The reusability of synthesized Cu2O-ZnO/cellulose composite photocatalysts was tested via a recycling experiment. After a photocatalytic cycle, the Cu2O-ZnO/cellulose composite was filtrated and purified in distilled water, aiming to fully remove the residual impurities. The reused Cu2O-ZnO/cellulose composite photocatalyst was obtained after the drying process in the vacuum oven at 60 °C for the next photodegradation test.

3.7. Reactive Species Trapping Experiments

Benzoquinone (BQ), Tert Butanol (TB), and KI were used as scavengers of superoxide anion radical (·O2), hydroxyl radical (·OH), and hole (h+), respectively, which aimed to further explore the photocatalytic mechanism of Cu2O-ZnO/cellulose composites. A total of 0.3 g of Cu2O-ZnO/cellulose composite was added to the methyl orange solution (C14H14N3NaO3S) (0.06 mmol/L, 15 mL), which contained 1 mmol/L of the quencher, and then followed by dark treatment for half an hour. The mixture was irradiated by a 6.6 W UV-vis lamp. A total of 1 mL liquid supernatant was taken out for testing at the selected time intervals and subsequently poured back into the reactor. The concentration changes in methyl orange were measured by the UV-vis spectrophotometer (TU-1900, PERSEE Corp., Taoyuan, China), with the main absorbance entered at 465 nm.

4. Conclusions

In this work, a Cu2O-ZnO/cellulose composite with stable and good photocatalysis has been successfully fabricated and applied in the photocatalytic degradation of pollutants of MO. ZnO nanoflowers and Cu2O nanospheres have been uniformly loaded on the cellulose fiber surface by employing the chemical precipitation method because of the dispersion and fixation of cellulose fiber. Therefore, the Cu2O-ZnO/cellulose composite possesses the highest separation efficiency of photogenic carrier and light absorption capacity. Moreover, the Cu2O-ZnO/cellulose composite has good photocatalytic activity for the degradation of MO dye and phenol pollutants because of the synergistic action of adsorption and photocatalysis. The as-prepared Cu2O-ZnO/cellulose composite can photodegrade 96% MO and 100% phenol within 80 min under UV-vis irradiation and it possesses excellent recycling activity and stability. After five cycles, the Cu2O-ZnO/cellulose composite can maintain 90% photodegradation efficiency. Overall, the high photocatalytic efficiency and recycling performance of Cu2O-ZnO/cellulose composites have been prepared, with the hope to provide a novel and efficient photocatalyst for wastewater treatment.

Author Contributions

Y.L.: Conceptualization, Methodology, Writing—original draft preparation, Investigation, Writing—Reviewing and Editing. M.Y.: Methodology, Writing—Reviewing and Editing, Supervision, Validation. X.L.: Investigation. J.M.: Methodology, Writing—Reviewing and Editing, Supervision, Validation. All authors have read and agreed to the published version of the manuscript.

Funding

We are grateful for financial support from the National Natural Science Foundation of China (No. 22378207) and the Metasequoia Faculty Start-up Research Fund of Nanjing Forestry University (163240006).

Data Availability Statement

The original data are included in the article. Further inquiries can be directly addressed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. Aladpoosh, R.; Montazer, M. Nano-Photo Active Cellulosic Fabric through in Situ Phytosynthesis of Star-like Ag/ZnO Nanocomposites: Investigation and Optimization of Attributes Associated with Photocatalytic Activity. Carbohydr. Polym. 2016, 141, 116–125. [Google Scholar] [CrossRef] [PubMed]
  2. Bagheri, M.; Rabieh, S. Preparation and Characterization of Cellulose-ZnO Nanocomposite Based on Ionic Liquid ([C4mim] Cl). Cellulose 2013, 20, 699–705. [Google Scholar] [CrossRef]
  3. Hoffmann, M.R.; Martin, S.T.; Choi, W.; Bahnemann, D.W. Environmental Applications of Semiconductor Photocatalysis. Chem. Rev. 1995, 95, 69–96. [Google Scholar] [CrossRef]
  4. Tokode, O.; Prabhu, R.; Lawton, L.A.; Robertson, P.K.J. Controlled Periodic Illumination in Semiconductor Photocatalysis. J. Photochem. Photobiol. A Chem. 2016, 319–320, 96–106. [Google Scholar] [CrossRef]
  5. Huang, M.H.; Mao, S.; Feick, H.; Yan, H.; Wu, Y.; Kind, H.; Weber, E.; Russo, R.; Yang, P. Room-Temperature Ultraviolet Nanowire Nanolasers. Science 2001, 292, 1897–1899. [Google Scholar] [CrossRef] [PubMed]
  6. Promdet, P.; Quesada-Cabrera, R.; Sathasivam, S.; Li, J.; Jiamprasertboon, A.; Guo, J.; Taylor, A.; Carmalt, C.J.; Parkin, I.P. High Defect Nanoscale ZnO Films with Polar Facets for Enhanced Photocatalytic Performance. ACS Appl. Nano Mater. 2019, 2, 2881–2889. [Google Scholar] [CrossRef]
  7. Yashni, G.; Al-Gheethi, A.; Mohamed, R.; Hossain, M.S.; Kamil, A.F.; Abirama Shanmugan, V. Photocatalysis of Xenobiotic Organic Compounds in Greywater Using Zinc Oxide Nanoparticles: A Critical Review. Water Environ. J. 2021, 35, 190–217. [Google Scholar] [CrossRef]
  8. Borzyszkowska, A.F.; Sulowska, A.; Zekker, I.; Karczewski, J.; Bester, K.; Zielińska-Jurek, A. Environmentally Friendly Fabrication of High-Efficient Fe-ZnO/Citric Acid-Modified Cellulose Composite and the Enhancement of Photocatalytic Activity in the Presence of H2O2. Catalysts 2022, 12, 1370. [Google Scholar] [CrossRef]
  9. Zhang, Z.; Yi, J.B.; Ding, J.; Wong, L.M.; Seng, H.L.; Wang, S.J.; Tao, J.G.; Li, G.P.; Xing, G.Z.; Sum, T.C.; et al. Cu-Doped ZnO Nanoneedles and Nanonails: Morphological Evolution and Physical Properties. J. Phys. Chem. C 2008, 112, 9579–9585. [Google Scholar] [CrossRef]
  10. Liu, X.; Huang, K.; Lin, X.; Li, H.; Tao, T.; Wu, Q.; Zheng, Q.; Huang, L.; Ni, Y.; Chen, L.; et al. Transparent and Conductive Cellulose Film by Controllably Growing Aluminum Doped Zinc Oxide on Regenerated Cellulose Film. Cellulose 2020, 27, 4847–4855. [Google Scholar] [CrossRef]
  11. Shi, C.; Zhang, L.; Bian, H.; Shi, Z.; Ma, J.; Wang, Z. Construction of Ag–ZnO/Cellulose Nanocomposites via Tunable Cellulose Size for Improving Photocatalytic Performance. J. Clean. Prod. 2021, 288, 125089. [Google Scholar] [CrossRef]
  12. Khan, R.; Hassan, M.S.; Cho, H.-S.; Polyakov, A.Y.; Khil, M.-S.; Lee, I.-H. Facile Low-Temperature Synthesis of ZnO Nanopyramid and Its Application to Photocatalytic Degradation of Methyl Orange Dye under UV Irradiation. Mater. Lett. 2014, 133, 224–227. [Google Scholar] [CrossRef]
  13. Abbasi, H.A.; Al Moneef, M.M.; Khan, J.; Hafeez, M.; Hameed, M.U.; Khan, M.A.; Shahida, S.; Abbasi, H.A.; Chang, S.-K. Unveiling the Exceptional Performance of ZnO/Zn2TiO4 Nanocomposites. Catalysts 2024, 14, 156. [Google Scholar] [CrossRef]
  14. Meng, A.; Xing, J.; Li, Z.; Wei, Q.; Li, Q. Ag/AgCl/ZnO Nano-Networks: Preparation, Characterization, Mechanism and Photocatalytic Activity. J. Mol. Catal. A Chem. 2016, 411, 290–298. [Google Scholar] [CrossRef]
  15. Li, H.; Zhang, L.; Lu, H.; Ma, J.; Zhou, X.; Wang, Z.; Yi, C. Macro-/Nanoporous Al-Doped ZnO/Cellulose Composites Based on Tunable Cellulose Fiber Sizes for Enhancing Photocatalytic Properties. Carbohydr. Polym. 2020, 250, 116873. [Google Scholar] [CrossRef] [PubMed]
  16. Huang, P.-S.; Qin, F.; Lee, J.-K. Role of the Interface between Ag and ZnO in the Electric Conductivity of Ag Nanoparticle-Embedded ZnO. ACS Appl. Mater. Interfaces 2020, 12, 4715–4721. [Google Scholar] [CrossRef] [PubMed]
  17. Li, J. Preparation of Highly Photocatalytic Active Nano-Size TiO2/Cu2O Particle Composites with a Novel Electrochemical Method. Electrochem. Commun. 2004, 6, 940–943. [Google Scholar] [CrossRef]
  18. Han, C.; Li, Z.; Shen, J. Photocatalytic Degradation of Dodecyl-Benzenesulfonate over TiO2–Cu2O under Visible Irradiation. J. Hazard. Mater. 2009, 168, 215–219. [Google Scholar] [CrossRef] [PubMed]
  19. Wang, Y.; She, G.; Xu, H.; Liu, Y.; Mu, L.; Shi, W. Cu2O Nanoparticles Sensitized ZnO Nanorod Arrays: Electrochemical Synthesis and Photocatalytic Properties. Mater. Lett. 2012, 67, 110–112. [Google Scholar] [CrossRef]
  20. Deo, M.; Shinde, D.; Yengantiwar, A.; Jog, J.; Hannoyer, B.; Sauvage, X.; More, M.; Ogale, S. Cu2O/ZnO Hetero-Nanobrush: Hierarchical Assembly, Field Emission and Photocatalytic Properties. J. Mater. Chem. 2012, 22, 17055. [Google Scholar] [CrossRef]
  21. Zhang, Z.; Shao, C.; Li, X.; Wang, C.; Zhang, M.; Liu, Y. Electrospun Nanofibers of p -Type NiO/n-Type ZnO Heterojunctions with Enhanced Photocatalytic Activity. ACS Appl. Mater. Interfaces 2010, 2, 2915–2923. [Google Scholar] [CrossRef] [PubMed]
  22. Nagaraju, G.; Ko, Y.H.; Yu, J.S. Facile Synthesis of ZnO/CuO Nanostructures on Cellulose Paper and Their p–n Junction Properties. Mater. Lett. 2014, 116, 64–67. [Google Scholar] [CrossRef]
  23. Udom, I.; Ram, M.K.; Stefanakos, E.K.; Hepp, A.F.; Goswami, D.Y. One Dimensional-ZnO Nanostructures: Synthesis, Properties and Environmental Applications. Mater. Sci. Semicond. Process. 2013, 16, 2070–2083. [Google Scholar] [CrossRef]
  24. Huang, X.; Li, G.; Cao, B.; Wang, M.; Hao, C. Morphology Evolution and CL Property of Ni-Doped Zinc Oxide Nanostructures with Room-Temperature Ferromagnetism. J. Phys. Chem. C 2009, 113, 4381–4385. [Google Scholar] [CrossRef]
  25. Bessekhouad, Y.; Brahimi, R.; Hamdini, F.; Trari, M. Cu2S/TiO2 Heterojunction Applied to Visible Light Orange II Degradation. J. Photochem. Photobiol. A Chem. 2012, 248, 15–23. [Google Scholar] [CrossRef]
  26. Lv, P.; Lin, L.; Zheng, W.; Zheng, M.; Lai, F. Photosensitivity of ZnO/Cu2O Thin Film Heterojunction. Opt.-Int. J. Light Electron Opt. 2013, 124, 2654–2657. [Google Scholar] [CrossRef]
  27. Prasad, N.; Karthikeyan, B. Cu-Doping and Annealing Effect on the Optical Properties and Enhanced Photocatalytic Activity of ZnO Nanoparticles. Vacuum 2017, 146, 501–508. [Google Scholar] [CrossRef]
  28. Zhang, L.; Shi, C.; Lu, H.; Li, H.; Zhou, X.; Wang, Z.; Ma, J. Porous Cellulose Gel-Regulated Flower-like ZnO-Cu Nanoparticles for Enhancing Interfacial Catalysis Activity and Recyclability in Environmental Catalysis. Appl. Surf. Sci. 2022, 597, 153737. [Google Scholar] [CrossRef]
  29. She, G.; Zhang, X.; Shi, W.; Cai, Y.; Wang, N.; Liu, P.; Chen, D. Template-Free Electrochemical Synthesis of Single-Crystal CuTe Nanoribbons. Cryst. Growth Des. 2008, 8, 1789–1791. [Google Scholar] [CrossRef]
  30. Jiang, T.; Xie, T.; Chen, L.; Fu, Z.; Wang, D. Carrier Concentration-Dependent Electron Transfer in Cu2O/ZnO Nanorod Arrays and Their Photocatalytic Performance. Nanoscale 2013, 5, 2938. [Google Scholar] [CrossRef]
  31. Li, Y.; Wang, J.; Yao, H.; Dang, L.; Li, Z. Efficient Decomposition of Organic Compounds and Reaction Mechanism with BiOI Photocatalyst under Visible Light Irradiation. J. Mol. Catal. A Chem. 2011, 334, 116–122. [Google Scholar] [CrossRef]
  32. Pirhashemi, M.; Habibi-Yangjeh, A. Ultrasonic-Assisted Preparation of Plasmonic ZnO/Ag/Ag2WO4 Nanocomposites with High Visible-Light Photocatalytic Performance for Degradation of Organic Pollutants. J. Colloid Interface Sci. 2017, 491, 216–229. [Google Scholar] [CrossRef] [PubMed]
  33. Fu, X.; Tang, W.; Ji, L.; Chen, S. V2O5/Al2O3 Composite Photocatalyst: Preparation, Characterization, and the Role of Al2O3. Chem. Eng. J. 2012, 180, 170–177. [Google Scholar] [CrossRef]
  34. Cao, C.; Xiao, L.; Liu, L.; Zhu, H.; Chen, C.; Gao, L. Visible-Light Photocatalytic Decolorization of Reactive Brilliant Red X-3B on Cu2O/Crosslinked-Chitosan Nanocomposites Prepared via One Step Process. Appl. Surf. Sci. 2013, 271, 105–112. [Google Scholar] [CrossRef]
  35. Shi, J.; Li, J.; Huang, X.; Tan, Y. Synthesis and Enhanced Photocatalytic Activity of Regularly Shaped Cu2O Nanowire Polyhedra. Nano Res. 2011, 4, 448–459. [Google Scholar] [CrossRef]
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Figure 1. (a) the SEM image of Cu2O-ZnO/cellulose composite, (b) the SEM image of ZnO/cellulose composite, (c) the SEM image of Cu2O/ZnO powder, (d) Cu and (e) Zn element mapping of Cu2O-ZnO/cellulose composite, and (f) the spectrum and element content of Cu2O-ZnO/cellulose composite.
Figure 1. (a) the SEM image of Cu2O-ZnO/cellulose composite, (b) the SEM image of ZnO/cellulose composite, (c) the SEM image of Cu2O/ZnO powder, (d) Cu and (e) Zn element mapping of Cu2O-ZnO/cellulose composite, and (f) the spectrum and element content of Cu2O-ZnO/cellulose composite.
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Figure 2. The composition and structure of samples. (a) XRD patterns, (b) FTIR spectra, and (c) XPS spectra of samples and high-resolution XPS spectra for (d) Zn2p, (e) O1s, and (f) Cu2p samples.
Figure 2. The composition and structure of samples. (a) XRD patterns, (b) FTIR spectra, and (c) XPS spectra of samples and high-resolution XPS spectra for (d) Zn2p, (e) O1s, and (f) Cu2p samples.
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Figure 3. (a) Adsorption equilibrium curves of prepared photocatalysts before the photocatalytic test; (b,c) kinetic linear simulation plots of ZnO/cellulose composite, Cu2O/ZnO powder, Cu2O-ZnO/cellulose composite, and blank sample for photodegradation of MO dye under UV-vis light irradiation; (d,e) kinetic linear simulation plots of ZnO/cellulose composite, Cu2O/ZnO powder, Cu2O-ZnO/cellulose composite, and blank sample for photodegradation of phenol dye under UV-vis light irradiation; (f) PL of spectra of ZnO/cellulose composite and Cu2O-ZnO/cellulose composite, and (g) experimental flow chart of catalytic degradation of MO under UV-vis.
Figure 3. (a) Adsorption equilibrium curves of prepared photocatalysts before the photocatalytic test; (b,c) kinetic linear simulation plots of ZnO/cellulose composite, Cu2O/ZnO powder, Cu2O-ZnO/cellulose composite, and blank sample for photodegradation of MO dye under UV-vis light irradiation; (d,e) kinetic linear simulation plots of ZnO/cellulose composite, Cu2O/ZnO powder, Cu2O-ZnO/cellulose composite, and blank sample for photodegradation of phenol dye under UV-vis light irradiation; (f) PL of spectra of ZnO/cellulose composite and Cu2O-ZnO/cellulose composite, and (g) experimental flow chart of catalytic degradation of MO under UV-vis.
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Figure 4. (a) UV-vis DRS spectra of the ZnO/cellulose, Cu2O/ZnO Powder, and Cu2O-ZnO/cellulose; (b) calculation of bandgap energy by Tauc equation using a plot of (αhν)2 vs. photon energy (hν). Trapping experiment of active species during the photocatalytic degradation of MO over the Cu2O-ZnO/cellulose in the presence of various scavengers under UV-vis irradiation; (c) photocatalytic degradation curves (C/C0) of MO; (d) linear fitting −ln (C/C0) of the kinetic curves, and (e) proposed mechanism of degradation and schematic representation of Cu2O/ZnO grown on the surface of cellulose.
Figure 4. (a) UV-vis DRS spectra of the ZnO/cellulose, Cu2O/ZnO Powder, and Cu2O-ZnO/cellulose; (b) calculation of bandgap energy by Tauc equation using a plot of (αhν)2 vs. photon energy (hν). Trapping experiment of active species during the photocatalytic degradation of MO over the Cu2O-ZnO/cellulose in the presence of various scavengers under UV-vis irradiation; (c) photocatalytic degradation curves (C/C0) of MO; (d) linear fitting −ln (C/C0) of the kinetic curves, and (e) proposed mechanism of degradation and schematic representation of Cu2O/ZnO grown on the surface of cellulose.
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Figure 5. Recyclability tests for Cu2O-ZnO/cellulose composite under UV-vis light irradiation for 80 min.
Figure 5. Recyclability tests for Cu2O-ZnO/cellulose composite under UV-vis light irradiation for 80 min.
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Figure 6. Flowchart of the preparation of the Cu2O-ZnO/cellulose composite.
Figure 6. Flowchart of the preparation of the Cu2O-ZnO/cellulose composite.
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Table 1. Comparison of photocatalytic performance of Cu2O-ZnO/cellulose composites for the degradation of pollutants of different models and related photocatalysts in recent years.
Table 1. Comparison of photocatalytic performance of Cu2O-ZnO/cellulose composites for the degradation of pollutants of different models and related photocatalysts in recent years.
LightCatalystPollutantModel Contamination
(k, min−1 × 10−1)		References
λ = 390TiO2/ZnO/HPMophenol0.02[13]
λ < 254TiO2phenol0.045[18]
300 < λ < 780ZnO/cellulosephenol0.013[2]
300 < λ < 780Cu2O/ZnOphenol0.04[17]
200 < λ < 800Cu2O/ZnO/cellulosephenol0.0625this work
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Li, Y.; Yan, M.; Li, X.; Ma, J. Construction of Cu2O-ZnO/Cellulose Composites for Enhancing the Photocatalytic Performance. Catalysts 2024, 14, 476. https://doi.org/10.3390/catal14080476

AMA Style

Li Y, Yan M, Li X, Ma J. Construction of Cu2O-ZnO/Cellulose Composites for Enhancing the Photocatalytic Performance. Catalysts. 2024; 14(8):476. https://doi.org/10.3390/catal14080476

Chicago/Turabian Style

Li, Yuchen, Ming Yan, Xin Li, and Jinxia Ma. 2024. "Construction of Cu2O-ZnO/Cellulose Composites for Enhancing the Photocatalytic Performance" Catalysts 14, no. 8: 476. https://doi.org/10.3390/catal14080476

APA Style

Li, Y., Yan, M., Li, X., & Ma, J. (2024). Construction of Cu2O-ZnO/Cellulose Composites for Enhancing the Photocatalytic Performance. Catalysts, 14(8), 476. https://doi.org/10.3390/catal14080476

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