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Article

Synthesis and Characterization of Ag-Ag2O/TiO2@polypyrrole Heterojunction for Enhanced Photocatalytic Degradation of Methylene Blue

by
Rajeev Kumar
1,
Reda M. El-Shishtawy
2,3 and
Mohamed A. Barakat
1,4,*
1
Department of Environmental Sciences, Faculty of Meteorology, Environment, and Arid Land Agriculture, King Abdulaziz University, Jeddah 21589, Saudi Arabia
2
Chemistry Department, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah, Saudi Arabia
3
Dyeing, Printing and Textile Auxiliaries Department, Textile Research Division, National Research Center, Dokki, Giza 12311, Egypt
4
Central Metallurgical R & D Institute, Helwan 11421, Cairo, Egypt
*
Author to whom correspondence should be addressed.
Catalysts 2016, 6(6), 76; https://doi.org/10.3390/catal6060076
Submission received: 30 March 2016 / Revised: 13 May 2016 / Accepted: 17 May 2016 / Published: 25 May 2016
(This article belongs to the Special Issue Photocatalytic Wastewater Treatment)
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Abstract

:
Hybrid multi-functional nanomaterials comprising two or more disparate materials have become a powerful approach to obtain advanced materials for environmental remediation applications. In this work, an Ag-Ag2O/TiO2@polypyrrole (Ag/TiO2@PPy) heterojunction has been synthesized by assembling a self-stabilized Ag-Ag2O (p type) semiconductor (denoted as Ag) and polypyrrole (π-conjugated polymer) on the surface of rutile TiO2 (n type). Ag/TiO2@PPy was synthesized through simultaneous oxidation of pyrrole monomers and reduction of AgNO3 in an aqueous solution containing well-dispersed TiO2 particles. Thus synthesized Ag/TiO2@PPy was characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and UV-Vis diffuse reflectance spectroscopy (UV-vis DSR). The photocatalytic activity of synthesized heterojunction was investigated for the decomposition of methylene blue (MB) dye under UV and visible light irradiation. The results revealed that π-conjugated p-n heterojunction formed in the case of Ag/TiO2@PPy significantly enhanced the photodecomposition of MB compared to the p-n type Ag/TiO2 and TiO2@PPy (n-π) heterojunctions. A synergistic effect between Ag-Ag2O and PPy leads to higher photostability and a better electron/hole separation leads to an enhanced photocatalytic activity of Ag/TiO2@PPy under both UV and visible light irradiations.

1. Introduction

Heterogeneous photocatalytic degradation of pollutants by an n-type semiconductor, i.e., TiO2 nanoparticles, has been widely studied in the last decade [1]. Rutile and anatase polymorphs of TiO2 are the most studied structures, among which anatase shows much higher photocatalytic activity [2]. Meanwhile, rutile TiO2 has low band-gap energy (~3.02 eV) compared to anatase TiO2 (~3.2), which allows it to absorb solar energy more efficiently than the anatase form, hence making it a suitable candidate for photocatalytic applications. However, the wide band gap of rutile TiO2 and poor quantum yield results in low photo efficiency, which limits its use in visible light [2,3]. In order to extend the photo response in visible light and improve the photocatalytic activity of TiO2, various doping, co-doping, composite, coupling, etc. techniques have been investigated and various materials with TiO2 such as carbon [4], Pt(II) [5], CoFe2O4 [6], N, Fe, Fe-N [7], Ag-polyaniline [8], etc. have gained much attention in the recent past. Among these, noble metals such as Au, Ag, Pt, etc. have shown high photocatalytic enhancing property by inhibiting charge carrier recombination within the semiconductor materials [9]. Silver (Ag0/Ag+) is one of the most promising noble metals used to make visible light photoactive materials. Ag2O is a p-type semiconductor with energy ~1.46 eV and has been widely used as photocatalyst in single, binary, or multiple composite systems [10,11]. Under UV light irradiation, Ag2O behaves as an effective e−-absorbing agent, while under visible light irradiation it acts as an efficient photosensitizer [10,11]. However, Ag2O is photosensitive but its instability under light irradiation (Ag2O→2Ag + 1/2O2) is the main problem associated with its photocatalytic uses. Wang et al. [10] reported that Ag2O shows higher stability in the presence of metallic Ag. In an Ag-Ag2O system, Ag acts as an electron scavenger, which prevents the reduction of Ag2O. Therefore, the Ag-Ag2O system may be an effective methodology to overcome stability problems [8,12]. Moreover, the Ag-Ag2O system may enhance photocatalytic activity, increase the lifetime of the photocatalyst, and inhibit the leaching and aggregation of nano-sized semiconductor particles into the water [7,13].
Recently, conducting polymers such as polypyrrole (PPy), polythiophene, and polyaniline have been used as photosensitizers to modify the photocatalyst semiconductors band. These polymers can efficiently donate electrons, act as hole transporters, have good interfacial electron transfer process, and prevent oxidation/reduction of metallic nanoparticles under visible light excitation [14,15]. Among these conducting polymers, PPy possesses high electrochemical reversibility, superior conductivity, and high polarizability, and can also be easily synthesized by electrochemical or chemical routes [14,16]. In addition, the high thermal and chemical stability of PPy makes it a promising material and a stable photosensitizer, which may enhance the photocatalytic activity of TiO2 [17]. Various reports on the photocatalytic applications of PPy-based materials such as AgCl/PPy, [18], PPy-TiO2-Fly ash [19], PPy/Bi2WO6 [12], etc. have shown high photocatalytic efficiency in visible light for the degradation of organic pollutants.
On the basis of the aforementioned considerations, it may be assumed that a multi-component nanocomposite of Ag-Ag2O, polypyrrole (PPy) and TiO2 would possess a narrow band gap and higher photocatalytic activity and thus might be successfully applied for visible light photocatalysis. Therefore, in this work, an Ag/TiO2@PPy nanocomposite was synthesized and characterized by various techniques. The photocatalytic activity of the as-synthesized nanocomposite was evaluated for the degradation of methylene blue (MB) in an aqueous solution under UV and visible light irradiation. The photocatalytic activity of Ag/TiO2@PPy was also compared with two component composites i.e., Ag/TiO2 and TiO2@PPy.
In this work, an aqueous medium was used for the synthesis of a self-stabilized Ag-Ag2O structure in the presence of pyrrole. In this synthesis, pyrrole acts as a reducing agent and undergoes oxidative polymerization in the presence of Ag+ in aquatic conditions. This reaction was conducted in the homogeneous TiO2 suspension to deposit Ag-Ag2O and PPy over the TiO2 surface. The main objective of this work is to stabilize and enhance the photocatalytic activity of Ag2O under solar irradiation. Ag2O, when photo-reduced to AgO, is unstable at room temperature and forms Ag0 and O2 (Ag2O→AgO + Ag, AgO→Ag + 1/2O2) [10]. Under light irradiation, photo-generated electrons and holes from the conduction band (CB) and valence band (VB) band of Ag2O, respectively, reduce Ag+ ions into metallic Ag and oxidize lattice O2− to O2. For the stabilization of Ag2O, the photo-generated electron and holes in Ag2O must be separated immediately before lattice O2− oxidation and lattice Ag+ reduction. For this purpose, simultaneous synthesis of Ag-Ag2O-PPy onto TiO2 has been done to stabilize and enhance the photocatalytic activity of Ag2O.

2. Results and Discussion

In this hybrid system, metallic Ag collects and channels the photo-generated electrons from Ag2O/TiO2 while PPy is assumed to transfer photo-generated holes to the solid–solution interface [10,20]. To confirm the existence of Ag-Ag2O and PPy in the Ag/TiO2@PPy heterostructure, XPS analysis was performed as shown in Figure 1. The high-resolution spectra for Ag 3d demonstrate that silver is present in more than one oxidation state. The peaks appearing at 367.63 and 373.65 eV correspond to the Ag 3d5/2 and Ag 3d3/2, respectively, representing silver in Ag+ (Ag2O) oxidation state. The other peaks of Ag 3d5/2 and Ag 3d3/2 peaks at 368.1 and 374.11 eV, respectively, with a separation of 6 eV, confirm the existence of silver in the Ag0 state. These binding energies values are in good agreement with the reported values for Ag0 and Ag2O [10,21,22]. The binding energies for 1 Os peaks located at 530.1, 531.66 and 533.84 eV are ascribed to the O2− in TiO2 and Ag2O, respectively [22,23]. The characteristic peaks (Ti4+) of Ti 2p3/2 and 2p1/2 appeared at 458.84 and 464.68 eV, respectively [22]. The C 1s peaks of PPy, corresponding to the binding energies at 285 and 286.09 eV, can be attributed to the C−C and C−N groups and the other C 1s peak at 289.05 eV is attributed to the electronic transition on PPy ring [24]. The characteristic spectrum of pyrrolylium nitrogen (−NH−) as N 1s’ single major component appears at 399.7 eV, while the N 1s peak in our case appeared at low binding energy i.e., at 397.38 eV, which may be due to the dehydrogenation of pyrrolylium nitrogen [25,26].
XRD spectra of Ag/TiO2 and Ag/TiO2@PPy heteroconjugation are shown in Figure 1f. The XRD analysis showed highly crystalline rutile phase of TiO2 (JCPDS card No. 01-071-0650) without other detectable impurities, suggesting that the presence of Ag2O-Ag and PPy did not change the lattice structure of TiO2. However, the peaks for Ag2O-Ag and PPy are not observed due to its low concentration. Similar explanations have also been reported by several other researchers for indistinct XRD peaks in their respective composite systems [27,28]. The crystallite size of Ag/TiO2 and Ag/TiO2@PPy hybrid structures were found to be in the ranges of 34.3–61.9 nm and 61.3–80.8 nm, respectively.
To study the surface morphology and presence of Ag in Ag/TiO2@PPy nanocomposite, SEM and TEM analysis were performed as shown in Figure 2. The SEM image (Figure 2a) shows the highly irregular shape of the nanocomposite with large globules of different sizes. A thorough examination at higher magnification (Figure 2b) clearly shows Ag particles deposited on the TiO2@PPy polymer system. The TEM images of Ag/TiO2@PPy (Figure 2c,d) clearly demonstrate that spherical Ag nanoparticles are immobilized on the PPy-coated TiO2, hence confirming the successful synthesis of an Ag/TiO2@PPy hybrid material.
The optical properties of Ag/TiO2, TiO2@PPy, and Ag/TiO2@PPy were studied by UV-visible diffusion reflectance spectroscopy and the spectra are shown in Figure 3. All the studied composites exhibit the sharp adsorption edge < 400 nm, indicating the strong light absorption capability in both UV and visible light ranges. The absorption band in the UV region i.e., >380 nm is the characteristic band of Ti-O [29]. The spectrum of TiO2@PPy and Ag/TiO2@PPy is above Ag/TiO2, which can be attributed to the π–π* transition of the polypyrrole backbone. The optical band gaps of Ag/TiO2, TiO2/PPy, and Ag/TiO2/PPy are 2.97, 2.89, and 2.91 eV, respectively. As observed from the band gap analysis, the incorporation of Ag and PPy onto TiO2 significantly narrowed the band gap energy. Therefore, the UV and visible light response of the hybrid materials improved, which will result in enhanced photocatalytic properties.
The photocatalytic activity of Ag/TiO2@PPy heterostructure was comparatively studied with Ag/TiO2 and TiO2@PPy by using MB as a model pollutant in aqueous solution under UV and visible light irradiation. The degradation of MB as a function of irradiation time is shown in Figure 4. From Figure 4, it can be seen that the degradation of MB in UV irradiation was higher compared to the visible light irradiation and the photocatalytic behavior followed the order: TiO2 < TiO2@PPy < Ag/TiO2 < Ag/TiO2@PPy. The observed higher photocatalytic activity of Ag/TiO2@PPy than TiO2@PPy, Ag/TiO2, and TiO2 may be due to the fact that PPy and Ag nanoparticles may act as an interfacial charge carrier in the Ag-TiO2-PPy system, which leads to the prevention of electron-hole (e−/h+) pair recombination, thereby increasing the photocatalytic activity. Moreover, the effectiveness of a ternary composite system (Ag/TiO2@PPy) was comparatively enhanced due to the synergistic effect of Ag (Ag-Ag2O), TiO2 and PPy [29,30]. On the basis of this study, the Ag/TiO2@PPy composite was used for further photocatalytic studies.
The solution pH plays an important role in the interaction of a dye with the photocatalyst surface and their degradation. The UV and visible light photocatalytic activity of Ag/TiO2@PPy as a function of initial dye solution pH are shown in Figure 5. The degradation of MB is strongly affected by the solution pH and it increased with the increase in the solution pH from 3.0 to 9.0. The maximum degradation was observed at pH 9.0 for both UV and visible light. The observed behavior could be explained on the basis of surface charge on the Ag/TiO2@PPy at different solution pH values. Lower degradation efficiency of Ag/TiO2@PPy for MB in acidic solution was due to protonation of Ag/TiO2@PPy (NH2+ in PPy), which generates a positive surface charge and shows electrostatic repulsion with the positively charged MB ions [31,32]. As the solution pH increases from acidic to alkaline, the surface charge starts to turn negative and degradation of MB increases. At pH 9.0, deprotonation of nitrogen atoms of PPy takes place and the surface of Ag/TiO2@PPy becomes negatively charged, which interacts with cationic MB ions electrostatically, resulting in an enhancement of the photocatalytic degradation of MB [31,33]. Besides electrostatic forces, π–π stacking, hydrogen bonding, and van der Waals forces are also expected to be involved in the interaction of MB with Ag/TiO2@PPy. Due to these forces, reasonable photocatalytic degradation of MB was observed at pH 5.0 and 7.0.
The rate constant for MB degradation was calculated using a first-order reaction kinetic model: ln(C/C0) = −kt. where C0 and C denotes the concentration of MB before and after photocatalysis, respectively; and k and t are the rate constant and irradiation time, respectively. The values of rate constant calculated from the linear relation of ln(C/C0) vs. t are mentioned in Table 1. It can be seen from Table 1 that the rate constant values increased with the increase in the solution pH, confirming that a higher pH was favorable for MB degradation in an aqueous solution. Hence, the efficiency of Ag/TiO2@PPy under UV irradiation was much higher than the visible light photocatalytic degradation of MB. These results are in agreement with the abovementioned data. The higher efficacy of Ag/TiO2@PPy under UV light irradiation is due to the higher photon absorption by all three components (Ag, TiO2, and PPy) while in visible light irradiation only Ag and PPy can be photo-excited [11].
The effect of initial MB concentration in aquatic solution was studied in the range of 4 to 20 mg/L, as depicted in Figure 6. At lower concentrations almost 100% degradation of MB was observed under UV and visible light irradiation. As the concentration of MB increased from 4 to 20 mg/L, the degradation efficiency decreased from 99.62% to 83.9% under UV irradiation, while in visible light the efficiency decreased from 99.37% to 18.85%. The reduction in the degradation rate of MB can be explained on the basis of the higher surface coverage of Ag/TiO2@PPy with MB ions, which suppressed the production of •OH radicals [34]. Moreover, the increase in the optical density of the MB solution as a consequence of increasing the concentration of MB results in a decrease in the light penetration in the solution. Therefore, fewer photons reach the Ag/TiO2@PPy surface due to the UV/visible light screening effect of MB itself. This effect reduces the generation of O2•− and •OH, which causes a decrease in the efficiency of the photocatalytic reaction [34,35].
The aforementioned results confirmed that a π-conjugated Ag/TiO2@PPy heterojunction photocatalyst has higher photocatalytic activity than Ag/TiO2 and TiO2@PPy under both UV and visible light irradiation. A schematic illustration for e−/h+ separation in Ag/TiO2@PPy heterojunction under UV and visible light irradiation have been shown in Figure 7. Under UV light irradiation, both Ag2O (Ag2O + hʋ→h+ + e−) and TiO2 (TiO2 + hʋ→h+ + e−) could be photo-excited to generate e− and h+ pairs, while under visible light Ag2O and PPy (PPy + hʋ→h+ + e−) [36] get excited due to the narrow band gap (1.3 eV and 2.5 eV), thereby producing e− and h+ pairs. The CB level of Ag2O has a higher positive potential (+0.2 eV vs. SHE) compared with the single electron reduction of O2 (−0.046 V vs. SHE). Therefore, photogenerated e− from Ag2O can be transferred by metallic Ag (Ag+/Ag: 0.7991 V, vs. SHE) to the O2 and thereby generate O2•−and •OH radicals (e− + O2+ H2O→O2•− + •OH) through a chain of reactions [10,21]. In the combined system Ag/TiO2@PPy, π orbital becomes the highest occupied molecular orbital (HOMO) and the lowest occupied molecular orbital level (LUMO) of PPy is energetically higher than the CB edge of rutile TiO2 (3.0 eV) [9]. When PPy is harvested in visible light, the photogenerated e− are transferred to the excited state and these e− can be readily injected into the CB of TiO2 and photogenerated h+ channeled by the PPy to the solid solution interface, which generates hydroxyl radicals (h+ + H2O→•OH + H+). The photogenerated e− trapped by the catalyst surface adsorbs H2O and O2, which produces superoxide radical anions (O2•−, OOH, and OH−), while photogenerated h+ reacts with OH− and H2O to generate HO• and H+ species [37]. As a result, Ag/TiO2@PPy had a fast charge separation and enhanced the life of e−/h+ recombination, resulting in higher and faster photocatalytic activity.

3. Materials and Methods

Titanium dioxide (rutile TiO2) from Alfa-Aesar (Beijing, China) was used as the photocatalyst support. Pyrrole and AgNO3 were purchased from Sigma-Aldrich (Taufkirchen, Germany), and used as received. Methylene blue (MB) [C16H18N3SCl) was purchased from Techno Pharma (Bahadurgarh, India). The aqueous solution of MB was prepared by dissolving 1 g of dye in 1 L solution and dilution was performed to get the desired concentration of MB for photocatalytic degradation studies.

3.1. Synthesis of Ag/TiO2 Nanocomposite

A mixture of rutile TiO2 (1.5 g) and 0.26 g AgNO3 (dissolved in 10 mL H2O) was mixed well and dried in an oven at 60 °C for 12 h. This mixture was then spread on the glass plate and placed under a UV lamp at a distance of 10 cm. Thereafter, the mixture was irradiated with 302 nm light source at room temperature for 6 h with occasional mixing to ensure homogeneity.

3.2. Synthesis of TiO2@PPy and Ag/TiO2@PPy Nanocomposite

For the synthesis of TiO2@PPy, first 1.5 g of rutile TiO2 was dispersed in 14 mL H2O at room temperature, to which 0.26 g AgNO3 (dissolved in 10 mL H2O) and 6 mL pyrrole solution was added and thereafter the entire system was put under stirring conditions. To the above dispersion of pyrrole, AgNO3, and TiO2, the solution of oxidant 0.27 g of FeCl3 (dissolved in 10 mL H2O) was added. A greenish-black color indicated the start of the polymerization process and the reaction was left to occur for 6 h. The resulting composite was thereafter filtered and washed with an excess of water, ethanol, and acetone to remove the PPy oligomers, unreacted oxidant, and other impurities. The prepared Ag/TiO2@PPy nanocomposite was dried in an air oven for 24 h at 80 °C and stored in a desiccator for its further use. A TiO2@PPy nanocomposite was also prepared similarly in the absence of AgNO3.

3.3. Characterization

The morphology of Ag/TiO2@PPy was studied by field emission scanning electron microscopy (FESEM) (JSM-7500 F; JEOL, Tokyo, Japan) and transmission electron microscopy (TEM) (model Tecnai G2 F20 Super Twin) at 200 kV with LaB6 emitter. The UV-vis spectra of Ag/TiO2, TiO2@PPy and Ag/TiO2@PPy were recorded with a Perkin Elmer UV-visible diffuse reflectance spectrophotometer in the range of 200–900 nm. X-ray photoelectron spectroscopy (XPS) measurements were recorded on a SPECS GmbH, (Berlin, Germany) spectrometer using a non-monochromatic Mg-Kα (1253.6 eV). X-ray source. X-ray diffraction (XRD) spectra of Ag/TiO2 and Ag/TiO2@PPy were recorded by an Ultima-IV (Rigaku, Japan) diffractometer using Cu Kα radiation.

3.4. Photocatalytic Activity

The photocatalytic degradation of MB under ultraviolet-C and visible light irradiation (112 W) was conducted in a 200-mL Pyrex beaker containing 100 mL dye solution under continuous aeration and magnetic stirring. The photocatalytic reactions at a fixed photocatalyst mass (0.1 g) were performed by varying the operational conditions such as solution pH (from 3 to 9), reaction time (between 5 and 180 min), and initial MB concentration (from 4 to 20 mg/L). Before starting the photocatalytic reactions, the solutions were kept in the dark for 30 min for the adsorption MB onto the materials and then the solutions were illuminated with UV/visible light. After photocatalytic reaction, the solutions were filtered through a 0.22-µm syringe filter and the amount of MB remaining in the supernatant solution was determined at a maximum wavelength of 665 nm using a HACH LANGE DR-6000 UV-visible spectrometer.

4. Conclusions

Ag/TiO2, TiO2@PPy, and Ag/TiO2@PPy nanocomposites were successfully synthesized. XPS studies indicated that Ag was present in metallic and ionic forms. The UV-visible absorption studies showed that all the synthesized composites are effective visible light sensitizers. Ag/TiO2@PPy showed superior photocatalytic activity in comparison to Ag/TiO2 and TiO2@PPy under UV and visible light. The superior photocatalytic activity of Ag/TiO2@PPy heterojunction may be due to the higher e−/h+ charge separation (there is a built-in electrostatic field at the heterojunction). PPy plays the role of photosensitizer and electron accepter in order to enhance the photodecomposition of MB in aquatic solution. The maximum photocatalytic activity of Ag/TiO2@PPy for MB was observed at pH 9 and the pseudo-first order rate constant values were 0.044 and 0.003 min−1 under UV and visible light irradiation, respectively. The effect of initial dye concentration revealed that the degradation of MB decreased from 100% to 18.85% under UV light and from 100% to 83% in visible light when the MB concentration increased from 4 to 20 mg·L−1. These results suggest that Ag/TiO2@PPy could be used as a promising material for the application of organic pollutant photodegradation in a vast variety of areas.

Acknowledgments

This project was supported by the NSTIP strategic technologies program in the Kingdom of Saudi Arabia – Project No (11-ENE1531-03). The authors also, acknowledge with thanks Science and Technology Unit, King Abdulaziz University for technical support.

Author Contributions

Mohamed A Barakat and Reda M. El-Shishtawy designed this work. Reda M. El-Shishtawy synthesized the materials. Rajeev Kumar conducted the experimental work and the manuscript was written by Rajeev Kumar and Mohamed A. Barakat.

Conflicts of Interest

The authors declare no conflict of interest.

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Figure 1. XPS analysis of Ag/TiO2@PPy (a–e) and XRD patterns of Ag/TiO2 and Ag/TiO2@PPy (f).
Figure 1. XPS analysis of Ag/TiO2@PPy (a–e) and XRD patterns of Ag/TiO2 and Ag/TiO2@PPy (f).
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Figure 2. Surface morphology of Ag/TiO2@PPy composite, SEM images (a,b) and TEM (c,d).
Figure 2. Surface morphology of Ag/TiO2@PPy composite, SEM images (a,b) and TEM (c,d).
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Figure 3. UV-vis spectra of Ag/TiO2, TiO2@PPy, and Ag/TiO2@PPy heterostructures.
Figure 3. UV-vis spectra of Ag/TiO2, TiO2@PPy, and Ag/TiO2@PPy heterostructures.
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Figure 4. Comparison of MB photocatalytic degradation efficiency of synthesized heterojunctions under (a) UV and (b) visible light irradiation.
Figure 4. Comparison of MB photocatalytic degradation efficiency of synthesized heterojunctions under (a) UV and (b) visible light irradiation.
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Figure 5. Effect of solution pH on MB photodecomposition using Ag/TiO2@PPy heterostructure under UV and visible light irradiation.
Figure 5. Effect of solution pH on MB photodecomposition using Ag/TiO2@PPy heterostructure under UV and visible light irradiation.
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Figure 6. Effect of initial dye concentration on MB photocatalytic degradation.
Figure 6. Effect of initial dye concentration on MB photocatalytic degradation.
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Figure 7. Schematic representation of possible electron/hole pair separation mechanism of the Ag-Ag2O/TiO2@PPy heterostructure under (a) UV and (b) visible light irradiation.
Figure 7. Schematic representation of possible electron/hole pair separation mechanism of the Ag-Ag2O/TiO2@PPy heterostructure under (a) UV and (b) visible light irradiation.
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Table
Table 1. First order rate constants for the degradation of MB using Ag/TiO2@PPy.
Table 1. First order rate constants for the degradation of MB using Ag/TiO2@PPy.
pHk (UV) (min−1)R2k (Visible) (min−1)R2
30.0000.8340.0000.488
50.0140.9870.0020.987
70.0240.9290.0030.955
90.0440.9680.0030.947

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Kumar, R.; El-Shishtawy, R.M.; Barakat, M.A. Synthesis and Characterization of Ag-Ag2O/TiO2@polypyrrole Heterojunction for Enhanced Photocatalytic Degradation of Methylene Blue. Catalysts 2016, 6, 76. https://doi.org/10.3390/catal6060076

AMA Style

Kumar R, El-Shishtawy RM, Barakat MA. Synthesis and Characterization of Ag-Ag2O/TiO2@polypyrrole Heterojunction for Enhanced Photocatalytic Degradation of Methylene Blue. Catalysts. 2016; 6(6):76. https://doi.org/10.3390/catal6060076

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Kumar, Rajeev, Reda M. El-Shishtawy, and Mohamed A. Barakat. 2016. "Synthesis and Characterization of Ag-Ag2O/TiO2@polypyrrole Heterojunction for Enhanced Photocatalytic Degradation of Methylene Blue" Catalysts 6, no. 6: 76. https://doi.org/10.3390/catal6060076

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