Sr2NiWO6 Double Perovskite Oxide as a Novel Visible-Light-Responsive Water Oxidation Photocatalyst

Photocatalytic Overall Water Splitting with a Solar-to-Hydrogen Conversion Efficiency Exceeding 2 % through Halide Perovskite

Photocatalytic water splitting using semiconductors is a promising approach for converting solar energy to clean energy. However, challenges such as sluggish water oxidation kinetics and limited light absorption of photocatalyst cause low solar-to-hydrogen conversion efficiency (STH). Herein, we develop a photocatalytic overall water splitting system using I3 -/I- as the shuttle redox couple to bridge the H2-producing half-reaction with the O2-producing half-reaction. The system uses the halide perovskite of benzylammonium lead iodide (PMA2PbI4, PMA=C6H5CH2NH2) loaded with MoS2 (PMA2PbI4/MoS2) as the H2 evolution photocatalyst, and the RuOx-loaded WO3 (WO3/RuOx) as the O2 evolution photocatalyst, achieving a H2/O2 production in stoichiometric ratio with an excellent STH of 2.07 %. This work provides a detour route for photocatalytic water splitting with the help of I3 -/I- shuttle redox couple in the halide perovskite HI splitting system and enlightens one to integrate and utilize multi catalytic strategies for solar-driven water splitting.

Engineering Ba2Bi2O6 Double Perovskite with La3+ for High Current Density Visible Light Photoelectrochemical Hydrogen Evolution

A Lanthanum ion (La3+) incorporation strategy is implemented to modify Ba2Bi2O6-based double perovskite photoelectrodes. X-ray diffraction (XRD) characterization shows that highly crystalline Ba2La0.4Bi1.6O6 double perovskites with the space group I2/m are successfully prepared. UV-vis absorption spectra and the Tauc-plot reveal an optical band gap Eg ≈1.57 ± 0.01 eV. A thickness dependence of the photoelectrodes photoelectrochemical (PEC) performance shows that the submicron (≈1 µm) 4-times spin-coated thin film photoelectrode displays strong p-type conductivity, which delivers an encouraging photocurrent density of 0.88 mA cm-2 at 0.25 VRHE under AM 1.5G illumination. 10-times coated and 20-times coated medium thick (125.8-197 µm) photoelectrodes that exhibit moderate p-type conductivity, show further enhanced photocurrent densities of 1.5 mA cm-2 at 0 VRHE. In contrast, charge recombination centers existing in a standard thick pellet (≈500 µm) Ba2La0.4Bi1.6O6 photoelectrode can quench photo-generated charge carriers and greatly undermine PEC activities. The approach to doping at the Bi(III) sites contrasts with earlier efforts that focus on doping at the Bi(V) sites and thus paves the way for further tailoring a family of novel promising photocathode materials for efficient solar-water conversion devices.

Development of a novel Ba2BiV3O11 photocatalyst with dual functions of both water oxidation and proton reduction performance

To overcome the limitation of photocatalysts with dual functionality of water oxidation and proton reduction, we proposed a novel bismuth-based Ba2BiV3O11 (BBVO) photocatalyst, which can simultaneously drive the proton reduction reaction under UV light and water oxidation reaction under visible light. After doping with sulfur through an in situ vulcanization strategy, the light absorption and charge separation efficiencies of the sulfur-doped BBVO were significantly improved, thus boosting its oxygen evolution activity (64 μmol h-1) by more than 16 times compared with independent BBVO. The experimental results demonstrate that BBVO can be employed as a very promising bismuth-based photocatalyst for solar energy conversion.

Polymer-enhanced perovskite oxide-based photocatalysts: a review

Oxide perovskites (OPs) have emerged as promising photocatalysts for numerous applications, such as energy conversion, renewable fuels, and environmental remediation. Although OPs are gaining traction, their efficacies are still hindered by low charge carrier mobility and poor stability. This study investigated the function of polymers actively participating in OP structures to improve the overall characteristics. An overview of the polymer-enhanced perovskite oxide photocatalyst (PEPOP) field was effectively reviewed. These PEPOPs were demonstrated in photovoltaics, pollutant degradation, and gas conversion and reduction. Nonetheless, additional research is needed to explore the potential of PEPOPs to establish their efficacy in photocatalytic applications. The technological improvements of PEPOPs were hindered by significant challenges related to stability and sensitivity. The urgency of this review was apparent due to the fast-paced nature of research in the field of photocatalysis. Recent breakthroughs and emerging applications highlight the need for a comprehensive overview of PEPOPs and their enhanced catalytic capabilities. Consequently, a broad outlook was provided for the current state of PEPOP-related studies, highlighting the potential of these materials for future applications.

Integrating Co(OH)2 nanosheet arrays on graphene for efficient noble-metal-free EY-sensitized photocatalytic H2 evolution

The development of an efficient noble-metal-free cocatalyst is the key to photocatalytic hydrogen production technology. In this study, hierarchical Co(OH)2 nanosheet array-graphene (GR) composite cocatalysts are developed. With Eosin Y (EY) as a photosensitizer, the optimal Co(OH)2-10%GR hybrid cocatalyst presents excellent photocatalytic activity with an H2 production rate of 17 539 μmol g-1 h-1, and the apparent quantum yield for hydrogen production can reach 12.8% at 520 nm, which remarkably surpasses that of pure Co(OH)2 and most similar hybrid cocatalyst systems. Experimental investigations demonstrate that the excellent photocatalytic activity of Co(OH)2-GR arises from its unique nanosheet array architecture, which can collaboratively expose rich active sites for photocatalytic hydrogen evolution and facilitate the migration and separation of photogenerated charge carriers. It is desired that this study would supply a meaningful direction for the rational optimization of the constitute and structure of cocatalysts to achieve efficient photocatalytic hydrogen generation.

Room-Temperature Synthesis of Carbon Dot/TiO2 Composites with High Photocatalytic Activity

Benefiting from the wide-range absorption and adjustable energy gap, carbon dots (C-dots) have attracted a great deal of attention and they have been used to sensitize semiconductor nanocomposites to boost the efficiency of energy conversion devices, while there is still a lack of fundamental understanding of the interaction between such materials and their influence on the catalytic activity on the reaction process. In this study, C-dots were used to modify TiO₂ to form a direct Z-scheme (DZS) junction for enhancement of the photocatalytic activity. The C-dot/TiO₂ composite was prepared by ultrasonication at room temperature through coupling between the Ti-O-C bond and electrostatic interaction. The C-dots can dramatically enhance the absorption of the composite by forming the DZS, and the composite is enabled to generate more free radicals, which facilitate ∼10 times higher photocatalytic activity compared to that of TiO₂. As a proof of concept, the as-prepared C-dot/TiO₂ was used for textile wastewater dye degradation. This study provides an efficient approach for room-temperature preparation of C-dot/TiO₂ composites with high photocatalytic activity.

Research progresses on the application of perovskite in adsorption and photocatalytic removal of water pollutants

The problem of global water pollution and scarcity of water resources is becoming increasingly serious. Multifunctional perovskites can well drive adsorption and photocatalytic reactions to remove water pollutants. There are many advantages of perovskites, such as abundant oxygen vacancies, easily tunable structural morphology, stable crystal state, highly active metal sites, and a wide photo response range. However, there are few reviews on the simultaneous application of perovskite to adsorption and photocatalytic removal of water pollutants. Thus, this paper discusses the preparation methods of perovskite, the factors affecting the adsorption of water environmental pollutants by perovskite, and the factors affecting perovskite photocatalytic water pollutants. The particle size, specific surface area, oxygen vacancies, electron-hole trapping agents, potentials of the valence band, and conduction band in perovskites are significant influencing factors for adsorption and photocatalysis. Strategies for improving the performance of perovskites in the fields of adsorption and photocatalysis are discussed. The adsorption behaviors and catalytic mechanisms are also investigated, including adsorption kinetics and thermodynamics, electrostatic interaction, ion exchange, chemical bonding, and photocatalytic mechanism. It summarizes the removal of water pollutants by using perovskites. It provides the design of perovskites as high-efficiency adsorbents and catalysts for developing new technologies.

Upconversion nanoparticles coupled with hierarchical ZnIn2S4 nanorods as a near-infrared responsive photocatalyst for photocatalytic CO2 reduction

Developing near-infrared responsive (NIR) photocatalysts is very important for the development of solar-driven photocatalytic systems. Metal sulfide semiconductors have been extensively used as visible-light responsive photocatalysts for photocatalytic applications owing to their high chemical variety, narrow bandgap and suitable redox potentials, particularly the benchmark ZnIn₂S₄. However, their potential as NIR-responsive photocatalysts is yet to be reported. Herein, for the first time demonstrated that upconversion nanoparticles can be delicately coupled with hierarchical ZnIn₂S₄ nanorods (UCNPs/ZIS) to assemble a NIR-responsive composite photocatalyst, and as such composite is verified by ultraviolet-visible diffuse reflectance spectra and upconversion luminescence spectra. As a result, remarkable photocatalytic CO and CH₄ production rates of 1500 and 220 nmol g^-1h^-1, respectively, were detected for the UCNPs/ZIS composite under NIR-light irradiation (λ ≥ 800 nm), which is rarely reported in the literature. The remarkable photocatalytic activity of the UCNPs/ZIS composite can be understood not only because the heterojunction between UCNPs and ZIS can promote the charge separation efficiency, but also the intimate interaction of UCNPs with hierarchical ZIS nanorods can enhance the energy transfer. This finding may open a new avenue to develop more NIR-responsive photocatalysts for various solar energy conversion applications.

Photocatalysis and perovskite oxide-based materials: a remedy for a clean and sustainable future

The massive use of non-renewable energy resources by humankind to fulfill their energy demands is causing severe environmental issues. Photocatalysis is considered one of the potential solutions for a clean and sustainable future because of its cleanliness, inexhaustibility, efficiency, and cost-effectiveness. Significant efforts have been made to design highly proficient photocatalyst materials for various applications such as water pollutant degradation, water splitting, CO2 reduction, and nitrogen fixation. Perovskite photocatalyst materials are gained special attention due to their exceptional properties because of their flexibility in chemical composition, structure, bandgap, oxidation states, and valence states. The current review is focused on perovskite materials and their applications in photocatalysis. Special attention has been given to the structural, stoichiometric, and compositional flexibility of perovskite photocatalyst materials. The photocatalytic activity of perovskite materials in different photocatalysis applications is also discussed. Various mechanisms involved in photocatalysis application from wastewater treatment to hydrogen production are also provided. The key objective of this review is to encapsulate the role of perovskite materials in photocatalysis along with their fundamental properties to provide valuable insight for addressing future environmental challenges.

Synergistic Effects of Redox Couples and Oxygen Vacancies Improve the Tetracycline Degradation Property of La2NiMnO6

Improving the e^- and h⁺ separation efficiency and promoting the production of more radicals is the key to improving the degradation efficiency of catalytic degradation of antibiotics. On the other hand, intermediate analysis of antibiotics in the dark adsorption and light irradiation process is very important to clarify the entire antibiotic degradation pathway. Here, the La₂NiMnO₆ (LNMO) catalyst was prepared by the sol-gel method and the calcination method. By changing the calcination temperature (800, 900, and 1000 °C), the LNMO-based catalysts were successfully formed, abbreviated as L-800, L-900, and L-1000. XPS measurements demonstrated the presence of Mn⁴⁺, Mn³⁺, Mn²⁺, and oxygen vacancies (OVs) in the LNMO-based catalysts. Analysis of PL, PC, EIS, and TR-PL demonstrated that L-900 had the highest separation efficiency and fastest carrier mobility. The LNMO-based catalysts were used to degrade tetracycline (TC). With the optimized catalyst L-900, the decomposition rate of TC reached 99.57% in 120 min. The entire TC degradation pathway was analyzed according to LC-MS measurements. Radical trap experiments and ESR technology revealed that the synergistic effect of Mn⁴⁺/Mn³⁺, Mn⁴⁺/Mn²⁺, and OVs not only effectively separated e^- and h⁺ but also facilitated the formation of superoxide radicals (^•O₂^-) to accelerate TC degradation. Radicals ^•OH, h⁺, and ^•O₂^- all contributed to TC deterioration in increasing order of importance. In addition, XPS measurements of the L-900 catalyst before and after use indicated that Mn⁴⁺/Mn³⁺, Mn⁴⁺/Mn²⁺, and OVs were not reactants but mediators of e^- and h⁺. Finally, the mechanism of TC degradation with the LNMO-based catalysts was discussed. This work provided new material for TC degradation in the wastewater.

Effects of iron substitution and anti-site disorder on crystal structures, vibrational, optical and magnetic properties of double perovskites Sr2(Fe1−xNix)TeO6

We report a new series of DP Sr2(Fe1−xNix)TeO6, which have different transition metal Fe and Ni on B sites, providing an opportunity to investigate their effect on crystal structure, vibrational, optical and magnetic properties.

Rational Design of a Two-Dimensional Janus CuFeO2+δ Single Layer as a Photocatalyst and Photoelectrode

The exfoliation of 2D nanomaterials from 3D multimetal oxides with a stable structure is a great challenge. Herein, a delafossite CuFeO_2+δ nanosheet becomes an open-layered structure by introducing excess oxygen so that the 2D Janus CuFeO_2+δ single layer can be further obtained by aqueous ultrasonic exfoliation. The 2D Janus CuFeO_2+δ single layer breaks the limitation of mirror symmetry, which is very beneficial to the effective separation of photogenerated electron-hole pairs. Serving as both a photoelectrode and a photocatalyst, the 2D Janus CuFeO_2+δ single layer/few layer remarkably enhances the photocatalytic activity with long-term stability: the photocurrent density is increased by 2-fold, and the rate of H₂ evolution is increased by 1.5-fold, in comparison with the counterpart of unexfoliated CuFeO_2+δ nanosheets. This work demonstrates that 2D nanomaterials can be directly exfoliated from 3D nanomaterials by rational composition and microstructure design, which is helpful in promoting the development of bimetallic-oxide-ene (BMOene) as a novel functional material.

Dye-Sensitized Fe-MOF nanosheets as Visible-Light driven photocatalyst for high efficient photocatalytic CO2 reduction

Dye-sensitized system holds great potential for the development of visible-light-responsive photocatalysts not only because it can enhance the light absorption and charge separation efficiency of the systems but also because it can tune the band structure of catalysts. Herein, two-dimensional (2D) Fe-MOF nanosheets (Fe-MNS) with a LUMO potential of 0.11 V (vs. RHE) was prepared. Interestingly, it has been found that when the 2D Fe-MNS catalyst was functionalized with visible-light-responsive [Ru(bpy)]₃²⁺ as a dye-sensitizer, the electrons from the [Ru(bpy)]₃²⁺ can effectively inject into the 2D Fe-MNS, which resulted in a negative shift of the LUMO potential of the 2D Fe-MNS to -0.15 V (vs. RHE). Consequently, the [Ru(bpy)]₃²⁺/Fe-MNS catalytic system exhibits a sound photocatalytic CO₂-to-CO activity of 1120 μmol g^-1h^-1 under visible-light-irradiation. The photocatalytic CO production was further ameliorated by regulating the electronic structure of the 2D Fe-MNS by doping Co ions, achieving a remarkable photocatalytic activity of 1637 μmol g^-1h^-1. This work further supports that the dye-sensitized system is an auspicious strategy worth exploring with different catalysts for the development of visible-light-responsive photocatalytic systems.

Sol-gel auto combustion synthesis, characterization, and application of Tb2FeMnO6 nanostructures as an effective photocatalyst for the discoloration of organic dye contaminants in wastewater

In this study, the auto-combustion sol-gel method was used to prepare novel Tb2FeMnO6 (TFMO) double perovskite nanoparticles. Chemical and natural fuels were used to achieve these particles with appropriate size. The resulting particles were examined via X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) techniques. Rietveld analysis was also performed to confirm the crystallinity and lattice parameters of the formed particles. The particles obtained in the presence of maleic acid were selected as the optimal sample (S4), and the particles obtained in the presence of pomegranate paste were chosen as the non-optimal sample (S8) in terms of size and morphology. Both particles were used to investigate the photocatalytic activity. Fourier transform infrared spectroscopy (FTIR), UV-Vis diffuse reflectance spectroscopy (DRS), and vibrating sample magnetometer (VSM) analyses and N2 adsorption/desorption isotherms were performed for both samples and the results were compared. Erythrosine and malachite green dyes in aqueous solutions were used as contaminants in the photocatalysis process. The results showed 22% and 20% discoloration for S4 and 41% and 30% discoloration for S8 in the presence of erythrosine and malachite green under visible light irradiation. The photocatalytic activity was investigated under UV light for S4, which showed 80% and 50% discoloration for erythrosine and malachite green, respectively. Investigating the photocatalytic activity of TFMO double perovskite nanoparticles showed that these nanoparticles could be a desirable option for mitigating water pollution.

Regulation of Ferroelectric Polarization to Achieve Efficient Charge Separation and Transfer in Particulate RuO2 /BiFeO3 for High Photocatalytic Water Oxidation Activity

Exploiting spontaneous polarization of ferroelectric materials to achieve high charge separation efficiency is an intriguing but challenging research topic in solar energy conversion. This work shows that loading high work function RuO₂ cocatalyst on BiFeO₃ (BFO) nanoparticles enhances the intrinsic ferroelectric polarization by efficient screening of charges to RuO₂ via RuO₂ /BFO heterojunction. This leads to enhancement of the surface photovoltage of RuO₂ /BFO single nanoparticles nearly 3 times, the driving force for charge separation and transfer in photocatalytic reactions. Consequently, efficient photocatalytic water oxidation is achieved with quantum efficiency as high as 5.36 % at 560 nm, the highest activity reported so far for ferroelectric materials. This work demonstrates that, unlike low photocurrent density in film-based ferroelectric devices, high photocatalytic activity could be achieved by regulating the ferroelectric spontaneous polarization using appropriate cocatalyst to enhance driving force for efficient separation and transfer of photogenerated charges in particulate ferroelectric semiconductor materials.