Developing sustainable, high-performance perovskites in photocatalysis: design strategies and applications

Solar energy is attractive because it is free, renewable, abundant and sustainable. Photocatalysis is one of the feasible routes to utilize solar energy for the degradation of pollutants and the production of fuel. Perovskites and their derivatives have received substantial attention in both photocatalytic wastewater treatment and energy production because of their highly tailorable structural and physicochemical properties. This review illustrates the basic principles of photocatalytic reactions and the application of these principles to the design of robust and sustainable perovskite photocatalysts. It details the structures of the perovskites and the physics and chemistry behind photocatalytic reactions and describes the advantages and limitations of popular strategies for the design of photoactive perovskites. This is followed by examples of how these strategies are applied to enhance the photocatalytic efficiency of oxide, halide and oxyhalide perovskites, with a focus on materials with potential for practical application, that is, not containing scarce or toxic elements. It is expected that this overview of the development of photocatalysts and deeper understanding of photocatalytic principles will accelerate the exploitation of efficient perovskite photocatalysts and bring about effective solutions to the energy and environmental crisis.

Photocatalytic reduction of 4-nitroaniline in aqueous solution using BiOCl/BiOBr/rGO ternary heterojunction under simulated UV-visible light irradiation

BiOCl/BiOBr/rGO ternary heterojunctions were synthesized and characterized, and their photocatalytic activities were examined. Three different rGO mass ratios were incorporated into BiOCl_75%BiOBr_25%; 1% rGO, 3% rGO, and 5% rGO, respectively. The successful incorporation of rGO into the composites was confirmed using powder X-ray diffraction (PXRD). Furthermore, calculated band gap, elemental composition, and composites' morphology were investigated using UV-visible (UV-Vis) diffuse reflectance spectroscopy (DRS), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM), respectively. The photocatalytic activities of the ternary heterojunctions were evaluated toward the photocatalytic reduction of 4-nitroaniline (4-NA) in aqueous solution. Experimental results reveal that rGO incorporation enhances the activity of the prepared heterojunction photocatalysts, where photocatalyst containing 5% rGO exhibited the highest activity achieving rate of 0.84 min^-1.

Oxygen Vacancy-Enhanced Ultrathin Bi2O3-Bi2WO6 Nanosheets' Photocatalytic Performances under Visible Light Irradiation

The oxygen vacancy caused by ultrathin structures would be introduced into the semiconductor photocatalyst to boost its photocatalytic activity. Herein, ultrathin Bi₂O₃-Bi₂WO₆ nanosheet composites have been successfully synthesized via a facile hydrothermal method. Compared to pure Bi₂WO₆ nanosheets, the Bi₂O₃-Bi₂WO₆ nanosheet composites possess abundant oxygen vacancies, which was confirmed by the positron annihilation spectra. The ultrathin Bi₂O₃-Bi₂WO₆ nanosheet composites exhibited remarkable photocatalytic degradation performance for oxytetracycline compared with that of pure Bi₂WO₆ nanosheets. The excellent photocatalytic activities of Bi₂O₃-Bi₂WO₆ composites could be attributed to the heterojunction structure and the oxygen vacancies caused by ultrathin structures.

Visible-Light-Activated C-C Bond Cleavage and Aerobic Oxidation of Benzyl Alcohols Employing BiMXO5 (M=Mg, Cd, Ni, Co, Pb, Ca and X=V, P)

The synthesis, structure, optical and photocatalytic studies of a family of compounds with the general formula, BiMXO₅ ; M=Mg, Cd, Ni, Co, Pb, Ca and X=V, P is presented. The compounds were prepared by regular solid-state reaction of constituents in the temperature range of 720-810 °C for 24 h. The compounds were characterized by powder X-ray diffraction (PXRD) methods. The Rietveld refinement of the PXRD patterns have been carried out to establish the structure. The optical absorption spectra along with the colors in daylight have been explained employing the allowed d-d transition. In addition, the observed colors of some of the V⁵⁺ containing compounds were explained using metal-to-metal charge transfer (MMCT) from the partially filled transition-metal 3d orbitals to the empty 3d orbitals of V⁵⁺ ions. The near IR (NIR) reflectivity studies indicate that many compounds exhibit good NIR reflectivity, suggesting that these compounds can be employed as 'cool pigments'. The experimentally determined band gaps of the prepared compounds were found to be suitable to exploit them for visible light activated photocatalysis. Photocatalytic C-C bond cleavage of alkenes and aerobic oxidation of alcohols were investigated employing visible light, which gave good yields and selectivity. The present study clearly demonstrated the versatility of the Paganoite family of compounds (BiMXO₅ ) towards new colored inorganic materials, visible-light photocatalysts and 'cool pigments'.

Photocatalytic production of dihydroxyacetone from glycerol on TiO2 in acetonitrile

In this paper, photocatalytic production of dihydroxyacetone (DHA) from glycerol in acetonitrile on TiO₂ was investigated. HPLC-MS analysis showed that glycerol was converted to DHA, glyceraldehyde (GAD), glyceric acid and several other chemicals. Using acetonitrile as the reaction medium instead of water not only provided a more selective process for production of DHA but also increased the glycerol conversion. After 300 min, with 1 g L⁻¹ catalyst loading and 4 mM initial glycerol concentration, glycerol conversion and DHA selectivity were 96.8% and 17.8% in acetonitrile compared to 36.1% and 14.7% in water, respectively. The half-life of glycerol decreased by a factor of 6.2, from 467 min to 75 min, by changing the solvent from water to acetonitrile. Experiments using biodiesel-derived crude glycerol verified the effectiveness of the proposed process for the photocatalytic production of DHA from crude glycerol. A mechanism was proposed to explain the higher selectivity towards DHA over GAD in this process.

Photocatalytic conversion of glycerol and selectivity for dihydroxyacetone production was increased by using acetonitrile as the reaction medium.

Formation of an oriented Bi2WO6 photocatalyst induced by in situ Bi reduction and its use for efficient nitrogen fixation

An in situ Bi reduction strategy to induce a preferential orientation that significantly enhanced the photocatalytic nitrogen fixation performance of Bi₂WO₆.

Application of metal oxide semiconductors in light-driven organic transformations

Herein, we provide an up-to-date overview of metal oxide semiconductors (MOS) as versatile and inexpensive photocatalysts to enable light-driven organic transformations.

Tuning the photocatalytic activity of bismuth wolframate: towards selective oxidations for the biorefinery driven by solar-light

The sol-gel entrapment of nanostructured Bi₂WO₆ enhances the activity and the selectivity of the short-gap semiconductor in the sunlight-driven photo-oxidation of trans-ferulic and trans-cinnamic acid dissolved in water with air as the primary oxidant. Valuable products such as vanillin, benzaldehyde, benzoic acid and vanillic acid are obtained. This provides the proof of concept that photocatalysis could be a promising technology in tomorrow's solar biorefineries.

Spatial separation of dual-cocatalysts on bismuth vanadate for selective aerobic oxidation of benzylalcohols to benzaldehydes under visible light irradiation

Efficient converting of alcohols to aldehydes under visible light can be achieved on BiVO₄ crystals with spatial separation of dual-cocatalysts.

Modification of heterogeneous photocatalysts for selective organic synthesis

This review elaborates on recent strategies of modifying heterogeneous photocatalysts for high-efficiency selective organic synthesis.

Antifouling and Photocatalytic Antibacterial Activity of the AquaSun Coating in Seawater and Related Media

Prolonged testing of the new xerogel photocatalytic coating AquaSun applied to a surface probe immersed in ocean water irradiated with simulated solar radiation shows excellent action against biofouling. Activated by moderate solar radiation, the organosilica film has also good antimicrobial properties. Considering the high stability, the environmental footprint, and the low cost of this sol-gel marine coating, the technology has significant potential toward replacing conventional antifouling and foul-release coatings with a single product of broad applicability.

CTAB-Assisted Fabrication of Bi₂WO₆ Thin Nanoplates with High Adsorption and Enhanced Visible Light-Driven Photocatalytic Performance

Two-dimensional thin Bi₂WO₆ nanoplates have been fabricated using a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method. We investigated the proposed formation mechanism based on the crystalline structures of the thin Bi₂WO₆ nanoplates. The high adsorption ability and excellent visible-light driven photocatalytic activities of the Bi₂WO₆ nanoplates were illustrated, in view of exposed (001) facets of nanoplates possessing faster separation of photo-generated charge carriers and increased catalytically active sites. Such a cost-effective way to obtain Bi₂WO₆ nanoplates offers new possibilities for the design of adsorptive semiconductor photocatalysts with strengthened photocatalytic activities.

Construction of Z-Scheme Bi2WO6/g-C3N4 Heterojunction Photocatalysts with Enhanced Visible-Light Photocatalytic Activity

Highly efficient visible-light-induced Z-scheme Bi2WO6/g-C3N4 heterojunction photocatalysts were synthesised by means of a simple hydrothermal method. The prepared Bi2WO6/g-C3N4 composite materials were characterised by means of X-ray diffraction, UV-vis diffuse reflectance spectroscopy, scanning electron microscopy, transmission electron microscopy, and photoluminescence. The photocatalytic activity of the Bi2WO6/g-C3N4 composite materials was determined through the degradation of Rhodamine B (RhB) solution as a target pollutant. The results of the experiment revealed that the active species O2•− and h+ play a crucial role in the scavenging system. The Bi2WO6/g-C3N4 composites showed an obviously improved photocatalytic performance compared with pure g-C3N4 and Bi2WO6 in the RhB degradation under visible light irradiation. The 10 wt-% Bi2WO6/g-C3N4 displayed the highest photocatalytic activity, and could completely degrade RhB within 75 min. It gave a reaction rate constant of 0.0439 min−1, which is 5.22 and 2.58 times higher than pure Bi2WO6 and g-C3N4, respectively. The intimate contact interface between the Bi2WO6 and g-C3N4 leads to effective separation of charge carriers and hinders the recombination efficiency of electrons and holes. Hence the photocatalytic activities of the Bi2WO6/g-C3N4 composite materials are significantly improved.

Constructing Bi24O31Cl10/BiOCl heterojunction via a simple thermal annealing route for achieving enhanced photocatalytic activity and selectivity

This work reports on the construction of a Bi₂₄O₃₁Cl₁₀/BiOCl heterojunction via a simple thermal annealing method. The X-ray diffraction (XRD) results indicated that the phase transformation from BiOCl to Bi₂₄O₃₁Cl₁₀ could be realized during the thermal annealing process. The high-resolution transmission electron microscopy (HRTEM) images, X-ray photoelectron spectroscopy (XPS) binding energy shifts, Raman spectra and Fouier transform infrared spectroscopy (FT-IR) spectra confirmed the formation of the Bi₂₄O₃₁Cl₁₀/BiOCl heterojunction. The obtained Bi₂₄O₃₁Cl₁₀/BiOCl photocatalyst showed excellent conversion efficiency and selectivity toward photocatalytic conversion of benzyl alcohol to benzaldehyde under visible light irradiation. The radical scavengers and electron spin resonance (ESR) results suggested that the photogenerated holes were the dominant reactive species responsible for the photocatalytic oxidation of benzyl alcohol and superoxide radicals were not involved in the photocatalytic process. The in-situ generation of Bi₂₄O₃₁Cl₁₀/BiOCl heterojunction may own superior interfacial contact than the two-step synthesized heterojunctions, which promotes the transfer of photogenerated charge carriers and is favorable for excellent photocatalytic activities.

Tuning the composition of Bi x W y O nanorods towards zero bias PEC water splitting

A unique co-oblique angle deposition method was used to create nanorod arrays of mixed phase Bi2O3/WO3/Bi2WO6 with varying atomic ratios of Bi to W. The effect of the tuning on the resulting nanostructures was characterized by EDX, SEM, XRD, optical transmission, specular reflection, and diffuse reflection spectroscopy. Samples with different Bi:W atomic ratio had a wide range of morphology and composition due to the surface mobility of deposited bismuth and its volume expansion during oxidation. Their photocatalytic and photoelectrochemical properties were investigated by methylene blue degradation and photo-generated current respectively. The sample with 38 at.% Bi showed the highest photodecay rates as well as the maximum photocurrent density, 4.3 μA cm(-2), at a bias potential of 600 mV versus Ag/AgCl (3M KCl); while the sample with 50 at.% Bi exhibited a high photocurrent density of 0.35 μA cm(-2) at zero bias potential, which indicates that varying the composition and mixed crystal phases of different oxides with appropriate band gaps and locations could hold the key to a visible light driven, zero bias potential, photoelectrochemical cell.

Amorphous Ti(iv)-modified Bi2WO6 with enhanced photocatalytic performance

Amorphous TiO₂ can function as an excellent hole cocatalyst to greatly improve the photocatalytic performance of a Bi₂WO₆ photocatalyst.

The application of heterogeneous visible light photocatalysts in organic synthesis

The recent advances of organic synthesis reactions based on heterogeneous visible-light photocatalysis are reviewed.

A green and efficient photocatalytic route for the highly-selective oxidation of saturated alpha-carbon C–H bonds in aromatic alkanes over flower-like Bi2WO6

A green and efficient photocatalytic route has been developed for the highly-selective oxidation of aromatic alkanes over flower-like Bi₂WO₆ under solvent-free conditions.

Enhanced photocatalytic activity of α-Fe2O3/Bi2WO6 heterostructured nanofibers prepared by electrospinning technique

One-dimensional α-Fe₂O₃/Bi₂WO₆ heterostructured nanofibers with the diameter of about 300–500 nm were successfully prepared by using a simple and straightforward protocol combining an electrospinning technique with a sintering process.

Enhanced photocatalytic activities of visible-light driven green synthesis in water and environmental remediation on Au/Bi2WO6 hybrid nanostructures

Deposition of Au NPs enhances photocatalytic activity toward selective oxidation of alcohol in water and Cr(vi) reduction over Bi₂WO₆ nanosheets.

In situ synthesis and excellent photocatalytic activity of tiny Bi decorated bismuth tungstate nanorods

Uniformly dispersed Bi in close contact with bismuth tungstate can enhance the photocatalytic efficiency of the bismuth tungstate.

One-step electrochemical synthesis of Bi3.84W0.16O6.24 with superior photocatalytic activities

Bi_3.84W_0.16O_6.24 nanoparticles were successfully prepared by a facile electrochemical route at room temperature in just 10 minutes.

Hierarchical flower-like Bi2WO6 hollow microspheres: facile synthesis and excellent catalytic performance

A one step method has been developed for the fabrication of hierarchical flower-like bismuth tungstate (Bi₂WO₆) hollow spheres via a solvothermal process.

Ionic liquid-assisted hydrothermal synthesis of Bi2WO6–reduced graphene oxide composites with enhanced photocatalytic activity

Due to the synergistic contributions of graphene and ionic liquid, the as-prepared RGO–Bi₂WO₆ samples exhibited the remarkably enhanced photocatalytic activities under visible light irradiation.

Nanochemistry-derived Bi2WO6 nanostructures: towards production of sustainable chemicals and fuels induced by visible light

The advances of Bi₂WO₆ nanostructures utilized in photocatalytic organic synthesis and fuel production under visible light are discussed and prospected.