Exclusive Papers by the Editorial Board Members and Topical Advisory Panel Members of Catalysts in the “Photocatalysis” Section

This Special Issue of Catalysts is dedicated to recent advances in the research areas of photocatalysts and photocatalyzed reactions. It comprises a diverse selection of seven exclusive papers by Editorial Board Members (EBMs) and Topical Advisory Panel (TAP) Members. The Special Issue focuses on highlighting novel, interesting investigations conducted in photocatalysis laboratories. The EBMs and TAP members represent the section as an attractive open-access publishing platform for research data on photocatalysts and photocatalyzed reactions.

In contribution 1, Chianese et al. focus on the use of gadolinium-doped bismuth ferrite for the photocatalytic oxidation of arsenite to arsenate under visible light. The effect of the gadolinium content was evaluated, and the 2 mol% content resulted in the highest photocatalytic efficiency in terms of As(V) production. The samples are thoroughly characterized in their optical, structural, and morphological properties. The study confirms that the main reactive oxygen species were O₂^−● and e⁻. A photocatalytic test was performed with a drinking water sample polluted by As(III), showing photocatalytic performance similar to that obtained in distilled water. It is concluded that gadolinium-doped bismuth ferrite can be considered an efficient photocatalytic material for the oxidation of As(III) to As(V) under visible light.

In contribution 2, Siliavka et al. analyze the effect of heterovalent Sc³⁺ and Nb⁵⁺ doping on the photoelectrochemical behavior of anatase TiO₂. The study details the doping effect on the work function, flat band potential, donor density, and the spectral dependence of the photocurrent and stationary photocurrent. The introduction of heterovalent doping results in higher conductivity and photoelectrochemical efficiency. In contrast to Nb doping, and according to theoretical predictions, Sc doping of TiO₂ results in the formation of deep, strongly localized states within the band gap with higher recombination efficiency, larger work function and flat band potential, and lower photoelectrochemical efficiency.

In contribution 3, Qi et al. report novel ternary composites, BiOBr–TiO₂–attapulgite (BTA), synthesized using a simple hydrothermal and water-bath method, that exhibit excellent photocatalytic performance for multiple xanthates. For the BTA photocatalyst, TiO₂ and BiOBr are uniformly loaded onto the surface of acid-activated attapulgite. As a widely used collector in mining processes, sodium ethyl-xanthate (SEX) was selected as the target pollutant due to its high toxicity. The BTA ternary photocatalyst demonstrated significantly higher adsorption and photocatalytic degradation performance compared to TiO₂ nanoparticles, BiOBr nanosheets, and the BiOBr–TiO₂ heterojunction. Structural characterization and experimental results indicated that the exceptional photocatalytic degradation efficiency of BTA was mainly attributed to the formation of a heterojunction between BiOBr and TiO₂, as well as the presence of additional active adsorption sites provided by attapulgite. Free radical scavenging experiments and EPR results confirm that the photogenerated holes are the predominant active species in photodegrading SEX. This work presents a novel approach to synthesizing mineral-based photocatalysts, which have broad prospects for application in flotation wastewater treatment.

One of the most widely analyzed research fields in photocatalysis is hydrogen generation. Photocatalytic H₂ production provides an ideal way to alleviate the energy crisis and solve environmental problems. In contribution 4, Sun et al. prepare metallic MoS₂/WS₂ dual co-catalysts through the in situ growth of 1T-WS₂ on the surface of 1T-MoS₂ via a solvothermal method. The ternary cross-linked MoS₂/WS₂/CdS photocatalysts are finally constructed by growing CdS nanorods on MoS₂/WS₂ co-catalysts. MoS₂/WS₂/CdS shows the lowest hydrogen evolution overpotential and the highest charge separation efficiency, due to the synergistic effect between WS₂ and MoS₂, which further accelerates the transfer of photogenerated electrons and inhibits the recombination of carriers. The hydrogen evolution rate of the MoS₂/WS₂/CdS composite is 12.12 mmol·g⁻¹·h⁻¹, which is 4.57 times that of pristine CdS.

In contribution 5, Xavier et al. report an optimized photocatalyst to remove the plasticizer and endocrine disruptor, bisphenol A (BPA), from water. The synthetic procedure includes the sonication of prepared particles of g-C₃N₄ and graphite oxide (rGO), followed by a reduction with hydrazine. In optimal conditions, the produced photocatalyst removes 90% of BPA in 90 min (30 min in the dark + 60 min irradiated) using a UV source, exhibiting pseudo-first-order kinetics. For comparison purposes, under the same experimental conditions, pure g-C₃N₄ removes only 50% of the BPA solution. Radical scavenging tests identify the superoxide radical as the main reactive oxygen species involved in the degradation. Two major degradation products were identified by mass spectrometry, both of them were less ecotoxic than the original BPA, according to in silico estimations (ECOSAR 2.0).

In contribution 6, Székely et al. synthesize Au/TiO₂/WO₃ heterostructures via heat- or time-assisted synthesis routes for photodegradation and dye sensing. They conclude that structural features, such as WO₃ crystalline phases, TiO₂ surface defects, and the WO₃ (220) to TiO₂-A (101) ratio, are the key parameters needed to obtain heterostructures with enhanced photocatalytic activity for removing oxalic acid, phenol, methyl orange, and aspirin. The most promising composite is Au/TiO₂/WO₃-HW-TA, and it yields conversion rates of 82.1, 95.9, and 96.8% for aspirin, oxalic acid, and phenol, respectively, with its detection limit for crystal violet as low as 10⁻⁸ M. The Au/TiO₂/WO₃ heterojunctions exhibited excellent stability as SERS substrates, yielding strong-intensity Raman signals of the pollutant molecules even after a long period of time.

Finally, Frédéric Dumur, in contribution 7, reviews the recent advances on furan-based visible light photoinitiators of polymerization. Photopolymerization is an active research field that enables polymerization in greener conditions than those performed with traditional thermal polymerization. At present, a great deal of effort is devoted to developing visible light photoinitiating systems. Indeed, traditional UV photoinitiating systems are currently the focus of numerous safety concerns; thus, alternatives to UV light are being actively researched. However, visible light photons are less energetic than UV photons, so the reactivity of the photoinitiating systems should be improved to address this issue. In this field, furane constitutes an interesting candidate for the design of photocatalysts for polymerization due to its low cost and easy chemical modification. In this review, an overview concerning the design of furane-based photoinitiators is provided. Comparisons with reference systems are also established to demonstrate evidence of the interest of these photoinitiators in innovative structures.

As can be seen, photocatalysis remains one of those hot research topics, covering a wide variety of applications such as water treatment, sensing, hydrogen generation, and the synthesis of high-value compounds. In the coming years, effort should be focused on the effect of the type of light irradiation, the immobilization of different substrates, and the search for photocatalysts that can overcome not only the photoactivity but also the simplicity of the benchmark photocatalyst, TiO₂. In this sense, there is still a long way to go, which would result in many more interesting studies like those collected in this Special Issue.