Trace Amount of SnO2-Decorated ZnSn(OH)6 as Highly Efficient Photocatalyst for Decomposition of Gaseous Benzene: Synthesis, Photocatalytic Activity, and the Unrevealed Synergistic Effect between ZnSn(OH)6 and SnO2

Surface Hydroxyl and Oxygen Vacancies Engineering in ZnSnAl LDH: Synergistic Promotion of Photocatalytic Oxidation of Aromatic VOCs

Photocatalytic oxidation has gained great interest in environmental remediation, but it is still limited by its low efficiency and catalytic deactivation in the degradation of aromatic VOCs. In this study, we concurrently regulated the surface hydroxyl and oxygen vacancies by introducing Al into ZnSn layered double hydroxide (LDH). The presence of distorted Al species induced local charge redistribution, leading to the remarkable formation of oxygen vacancies. These oxygen vacancies subsequently increased the amount of surface hydroxyl and elongated its bond length. The synergistic effects of surface hydroxyl and oxygen vacancies greatly enhanced reactant adsorption-activation and facilitated charge transfer to generate •OH, •O2-, and 1O2, resulting in highly efficient oxidation and ring-opening of various aromatic VOCs. Compared with commercial TiO2, the optimized ZnSnAl-50 catalyst exhibited about 2-fold activity for the toluene and styrene degradation and 10-fold activity for the chlorobenzene degradation. Moreover, ZnSnAl-50 demonstrated exceptional stability in the photocatalytic oxidation of toluene under a wide humidity range of 0-75%. This work marvelously improves the photocatalytic efficiency, stability, and adaptability through a novel strategy of surface hydroxyl and oxygen vacancies engineering.

Current trends on dry photocatalytic oxidation technology for BTX removal: Viable light sources and highly efficient photocatalysts

One of the main gaseous pollutants released by chemical production industries are benzene, toluene and xylene (BTX). These dangerous gases require immediate technology to combat them, as they put the health of living organisms at risk. The development of heterogeneous photocatalytic oxidation technology offers several viewpoints, particularly in gaseous-phase decontamination without an additional supply of oxidants in air at atmospheric pressure. However, difficulties such as low quantum efficiency, ability to absorb visible light, affinity towards CO2 and H2O synthesis, and low stability continue to limit its practical use. This review presents recent advances in dry-phase heterogeneous photodegradation as an advanced technology for the practical removal of BTX molecules. This review also examines the impact of low-cost light sources, the roles of the active sites of photocatalysts, and the feasible concentration range of BTX molecules. Numerous studies have demonstrated a significant improvement in the efficiency of the photodegradation of volatile organic compounds by enhancing the photocatalytic reactor system and other factors, such as humidity, temperature, and flow rate. The mechanism for BTX photodegradation based on density functional theory (DFT), electron paramagnetic resonance (EPR) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) investigations is also discussed. Finally, the present research complications and anticipated future developments in the field of heterogeneous photocatalytic oxidation technology are discussed.

Enhanced photocatalytic activity of cubic ZnSn(OH)6 by in-situ partial phase transformation via rapid thermal annealing

In this study, a mixed phase ZnSn(OH)₆/ZnSnO₃ photocatalyst was synthesized by calcining ZHS nanostructures via rapid thermal annealing (RTA) process. The composition ratio of ZnSn(OH)₆/ZnSnO₃ was controlled by changing the duration of the RTA process. The obtained mixed-phase photocatalyst was characterized by X-ray diffraction, field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, UV-vis diffuse reflectance spectroscopy, ultraviolet photoelectron spectroscopy, photoluminescence, and physisorption analysis. Results showed that ZnSn(OH)₆/ZnSnO₃ photocatalyst obtained by calcining ZHS at 300 °C for 20 s displayed the best photocatalytic performance under UVC light illumination. Under optimized reaction conditions, ZHS-20 (0.125 g) demonstrated nearly complete removal (>99%) of MO dye in 150 min. Scavenger study revealed the predominant role of OH^• in photocatalysis. The enhanced photocatalytic activity of the ZnSn(OH)₆/ZnSnO₃ composites was mainly ascribed to the photosensitization of ZHS by ZTO and effective electron-hole separation at the ZnSn(OH)₆/ZnSnO₃ heterojunction interface. It is expected that this study will provide new research input for the development of photocatalyst through thermal annealing-induced partial phase transformation.

Amorphous SnO2 decorated ZnSn(OH)6 promotes interfacial hydroxyl polarization for deep photocatalytic toluene mineralization

Surface hydroxyl groups play a decisive role in the generation of hydroxyl radicals with stronger oxidizing ability, which is indispensable in photocatalytic VOCs removal, especially under the condition of low humidity. In this work, non-noble amorphous SnO₂ decorated ZnSn(OH)₆ (ZSH) was synthesized by an in-situ method. The charge transport, reactant activation and hydroxyl polarization are enhanced through decoration of amorphous SnO₂ on ZSH. Combined with the designed experiment, in-situ EPR, DTF calculation and in-situ DRIFTS, the role and mechanism of interfacial hydroxyl polarization are revealed on SnO₂ decorated ZnSn(OH)₆. Compared with pristine ZSH and noble-metal modified ZSH, the toluene degradation rate of amorphous SnO₂ decorated ZSH is increased by 13.0 and 3.8 times, and the toluene mineralization rate is increased by 5.2 and 2.2 times. The ZSH-24 sample maintains a high toluene degradation activity after 6 cyclic utilization without catalyst deactivation. This work emphasizes the role of non-noble metal and the origin of hydroxyl group polarization on ZnSn(OH)₆ for photocatalytic VOCs mineralization.

Zinc hydroxystannate/zinc-tin oxide heterojunctions for the UVC-assisted photocatalytic degradation of methyl orange and tetracycline

Partial phase modification of zinc hydroxystannate (ZHS) is an effective technique for improving its light absorption capacity. In this study, a zinc hydroxystannate/zinc-tin oxide (ZHS/ZTO) heterostructure was synthesized via chemical co-precipitation followed by annealing. The as-prepared heterostructure revealed cubic crystal morphology along with high-intensity diffraction peaks in the XRD pattern. The XPS analysis of ZHS/ZTO heterostructures demonstrated the presence of key elements (Zn, Sn, and O) in their most stable ionic forms. The photocatalytic degradation efficiencies of the prepared samples were tested against methyl orange (MO) and tetracycline (TC) in an aqueous medium under UVC (254 nm) radiation. Under optimized conditions, maximum degradation efficiencies of 99% for MO and 97% for TC were observed in 120 and 180 min, respectively. Further, the predominant role of OH˙ radicals in the photocatalytic removal of MO and TC was evident through scavenging experiments. 2nd order kinetic model was outperformed in simulating the degradation mechanism of both targets over 1st and zero-order kinetic models. Finally, a photocatalytic degradation mechanism is proposed based on the energy values estimated for the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) using UPS analysis.

Sn1/3Na2/3Sn(OH)6 Perovskite with Sn4+/Na+ Disorder for Photocatalytic Degradation of 2,4-Dichlorophenol

Cation disorder in hydroxide-based perovskites remains relatively under-researched. In this work, novel hydroxide-based perovskite Sn_1/3Na_2/3Sn(OH)₆ was first fabricated by a direct hydrothermal method, and its ability to photodegrade 2,4-dichlorophenol was evaluated. The synthesized photocatalyst is isostructural with MSn(OH)₆ (M = Mg, Ca, Sr, Mn, Fe, Co, Ni, or Zn), where the M site is occupied by disordered Sn⁴⁺/Na⁺. Sn_1/3Na_2/3Sn(OH)₆ exhibits outstanding photocatalytic activity under ultraviolet light. Specifically, 99% of 2,4-DCP is photodegraded in 40 min, with approximately 94% of its total chlorine content converted to Cl^- anions. Radical trapping experiments indicated that superoxide radical anions (·O₂^-) play a critical role during the photocatalytic process. Finally, liquid chromatography-tandem mass spectrometry was conducted to monitor the photocatalytic intermediates. Overall, our findings demonstrate that hydroxide-based perovskites with cation disorder show promise for application in photocatalysis.

Accelerating Nickel-Based Molecular Construction via DFT Guidance for Advanced Photocatalytic Hydrogen Production

Understanding the nickel-based molecular catalyst structure and functional relationship is crucial for catalytic hydrogen production in aqueous solutions. Density functional theory (DFT) provides mature theoretical knowledge for efficient catalyst design, significantly reducing catalyst synthesis time and energy consumption. In the present work, three molecular catalysts, Ni(qbz)(pys)₂ (qbz = 2-quinoline benzimidazole) (NQP 1), Ni(qbo)(pys)₂ (qbo = 2-quinoline benzothiazole) (NQP 2), and Ni(pbz)(pys)₂ (pbz = 4-chloro-2,2-pyridylbenzimidazole) (NQP 3) (pys = 2-mercaptopyridine), were designed and synthesized and exhibit a high performance for H₂ generation in aqueous solution with a lamp (λ ≥ 400 nm) under visible light irradiation. Under the optimal conditions, a H₂ evolution rate as high as 1190 μmol h^-1 can be obtained over 25 mg of NQP 1 with the best catalytic performance. DFT has been adopted in this study to unveil the relationship between the ligand qbz and catalyst NQP 1─an efficient step in the design of catalysts with an excellent catalytic performance. We show that, in addition to the presence of the triphenyl ring increasing the overall electron density, rapid electron transfer (ET) from excited fluorescein (Fl) to NQP 1 significantly improves the chance of photogenerated electrons transferring to the active site, ultimately increasing the catalytic activity for H₂ production. This work on understanding the correlation between structures and properties of complexes provides a new idea for manufacturing high-performance photocatalysts.

Doping and facet effects synergistically mediated interfacial reaction mechanism and selectivity in photocatalytic NO abatement

The surface atomic coordination and arrangement largely determine photocatalytic properties. Whereas, the intrinsic impact of surface microstructures on the reaction mechanism and pathway is still unclear. Herein, via constructing N-doped Bi₂O₂CO₃ photocatalysts with diverse exposed facets, (1 1 0) and (0 0 1) facet, we testify that the pivotal roles of crystal facet and doping effect on the intermediate production and reactivity for photocatalytic nitric oxide (NO) abatement. The photoreactivity of N-doped Bi₂O₂CO₃ is documented to be higher than that of the pure samples because of the enhanced light absorption and charge transfer. Further in situ probing experiments and theoretical calculations verify that the unique adsorption patterns and activated intermediates on the (1 1 0) facet facilitate the formation of final products and inhibit the generation of toxic NO₂ by-product in terms of thermodynamics. More importantly, we found that the selective and nonselective oxidation processes are emerged over (1 1 0) and (0 0 1) facets of Bi₂O₂CO₃, respectively.

Synthesis of BiPO4 by crystallization and hydroxylation with boosted photocatalytic removal of organic pollutants in air and water

Environmental photocatlytsis has been considered as a promising alternative strategy to address the current environmental threats and pressures. Fabrication of the photocatalysts with high efficiency, stability and bio-safety is the core of photocatalytic applications. Herein, we report a facile approach to synthesize monazite BiPO₄ (SHTW) with high crystallization and hydroxylation. The wide bandgap of the SHTW can provide strong redox abilities to produce reactive species and mineralize organic pollutants. Its high crystallinity and dipole moment can promote separation and transportation of the photoexcited electron-hole pairs effectively. In addition, the hydroxylation can produce more highly oxidizing hydroxyl radicals and further improve charge carrier separation. Notably, the hydroxylation can be reborn and the high crystallization can be maintained during photocatalysis. Thus, a virtuous cycle can be established and organic pollutants can be removed efficiently. The mineralization rate of 146.1 μmol g^-1 h^-1 can be obtained on the SHTW for photocatalytic degradation of benzene, which is about 8.5 times higher than that of the commercial TiO₂ (P25). Various dyes, dyes mixture and bisphenol A can all be completely degraded over the SHTW. It shows the potential application and value in environmental governance.

Agro-waste extracted cellulose supported silver phosphate nanostructures as a green photocatalyst for improved photodegradation of RhB dye and industrial fertilizer effluents

The efficiency and reusability of photocatalysts are the dominant factors for their pragmatic use. The visible light induced semiconductor silver phosphate is a superior photocatalyst effective under visible light but its stability is still an undiscussed issue. To overcome this stability issue in this present manuscript, eco-friendly agro-waste extracted cellulose supported silver phosphate nanostructures have been designed for the first time through a simple chemical process. At first, silver phosphate nanostructures were synthesized by the co-precipitation method. Then, different weights of cellulose were added to the silver nitrate solution to form cellulose supported silver phosphate nanostructures. The photodegradation efficiency for each weight ratio was examined in which the photocatalyst Ag-8 nanostructures showed a high rate (0.024 min^-1) for degradation of Rhodamine B (RhB) using a low intensity tungsten bulb. Real sample analysis has also been carried out using this photocatalyst for the degradation of industrial fertilizer effluents. The degradation rate of all the nanostructures was found to be high in comparison to pristine silver phosphate as well as the extracted bare cellulose. The photocatalytic activity is enhanced because of the participation of cellulose as a support which makes an interface for silver phosphate and assists it in delaying the charge recombination period under visible light. To understand the photochemical reaction of electrons and holes, scavenger studies were also performed.

Ultrasmall BiOI Quantum Dots with Efficient Renal Clearance for Enhanced Radiotherapy of Cancer

Emerging strategies involving nanomaterials with high-atomic-number elements have been widely developed for radiotherapy in recent years. However, the concern regarding their potential toxicity caused by long-term body retention still limits their further application. In this regard, rapidly clearable radiosensitizers are highly desired for practical cancer treatment. Thus, in this work, ultrasmall BiOI quantum dots (QDs) with efficient renal clearance characteristic and strong permeability inside solid tumor are designed to address this issue. Additionally, considering that injection methods have great influence on the biodistribution and radiotherapeutic efficacy of radiosensitizers, two common injection methods including intratumoral injection and intravenous injection are evaluated. The results exhibit that intratumoral injection can maximize the accumulation of radiosensitizers within a tumor compared to intravenous injection and further enhance radiotherapeutic efficacy. Furthermore, the radiosensitizing effect of BiOI QDs is revealed, which is not only attributed to the radiation enhancement of high-Z elements but also is owed to the •OH production via catalyzing overexpressed H2O2 within a tumor by BiOI QDs under X-ray irradiation. As a result, this work proposes a treatment paradigm to employ ultrasmall radiosensitizers integrated with local intratumoral injection to realize rapid clearance and high-efficiency radiosensitization for cancer therapy.

Hybridization of CuO with Bi2MoO6 Nanosheets as a Surface Multifunctional Photocatalyst for Toluene Oxidation under Solar Irradiation

Herein, CuO/Bi₂MoO₆ hybrid nanosheets were prepared as a surface multifunctional photocatalyst for gas-phase toluene oxidation with high conversion (>99%). Aberration-corrected scanning transmission electron microscopy suggested that CuO species were highly dispersed on the nanosheets. X-ray absorption fine structure spectra indicated that the distorted and stretched Cu-O coordination structures in CuO/Bi₂MoO₆ nanosheets would provide open active sites. In situ Fourier transform infrared and density functional theory results showed that toluene molecules could be chemisorbed and activated on the active sites of CuO/Bi₂MoO₆ nanosheets by the C-H group forming CuO/Bi₂MoO₆···Ph-CH₃ surface complex compounds. These would induce electron-hole transfer and initiate photocatalytic reactions under visible light irradiation. The corresponding intermediates of benzaldehyde and benzoic acid would be detected by in situ diffuse reflectance infrared Fourier transform spectroscopy. Furthermore, the synergistic effect of CuO and Bi₂MoO₆ nanosheets could monitor charge dynamics to facilitate their respective transmission from photoexcitation sites to active centers. This work provides new insights into the essence of visible-light-driven surface photocatalysis and is expected to promote the design of novel and more effective photocatalysts at the molecular level.

Modifications of heterogeneous photocatalysts for hydrocarbon C–H bond activation and selective conversion

This feature article summarizes the recent progress in the modification of heterogeneous photocatalysts for photocatalytic hydrocarbons’ C–H bond activation.

Self-Assembly of CdS/CdIn2S4 Heterostructure with Enhanced Photocascade Synthesis of Schiff Base Compounds in an Aromatic Alcohols and Nitrobenzene System with Visible Light

A series of novel CdS/CdIn₂S₄ composite materials were prepared via a one-pot solvothermal process. The as-obtained photocatalysts were characterized by several techniques and the photocatalytic properties of CdS/CdIn₂S₄ photocatalysts were studied by photocascade synthesis of Schiff base compounds in a photocatalytic reaction system of aromatic alcohols and nitrobenzene irradiated with visible light. The results reveal that the resulting CdS/CdIn₂S₄ heterostructure samples show outstanding photocatalytic activities toward the photocascade production of Schiff base compounds in an aromatic alcohols and nitrobenzene reaction system irradiated with visible light. An optimized 50.0% CdS/CdIn₂S₄ heterostructure sample shows the highest Schiff base yield of 42.0% irradiated with visible light for 4 h, which is approximately 19.1 and 1.54 times higher than those of sole CdS and CdIn₂S₄ samples, respectively. The fabrication of heterogeneous structure improves the spatial separation and migration of photoinduced electron-hole pairs, thus contributing to the enhancement of photocatalytic properties. We foresee that this finding can offer a strategy to develop heterostructure composites for efficient synthesis of organics by photocatalysis under mild conditions.

Enhancing the photocatalytic activity of ZnSn(OH)6 achieved by gradual sulfur doping tactics

To solve the intrinsic deficiency inherited from the large band gap of ZnSn(OH)6 (ZSH), a gradual sulfur doping strategy is first proposed here to expand the optical absorption range, improve the separation efficiency of photogenerated electron-hole pairs, and thus enhance the photocatalytic activity. It is demonstrated that the distribution of sulfur in the flower-like ZSH (the sulfur doped sample is denoted as S-ZSH) tends to be largest on the outer most surface and becomes smaller towards the interior. The S-ZSH therefore has a gradual bandgap structure that is beneficial for transferring photogenerated charge carriers from the interior to the surface, which will greatly enhance the utilization of photoelectrons. As a result, the visible light photocurrent density of S-ZSH and the photocatalytic degradation rate of rhodamine (RhB) are about 5 and 10 times higher than with pristine ZSH, respectively.

Solvothermal synthesis of CdIn2S4 photocatalyst for selective photosynthesis of organic aromatic compounds under visible light

Ternary chalcogenide semiconductor, cadmium indium sulfide (CdIn₂S₄), was prepared by a simple solvothermal method using ethylene glycol as a solvent, as well as indium chloride tetrahydrate (InCl₃^.4H₂O), cadmium nitrate tetrahydrate [Cd(NO₃)₂^.4H₂O], and thiacetamide (TAA) as precursors. The resulted sample was subject to a series of characterizations. It is the first time to use CdIn₂S₄ sample as a visible light-driven photocatalyst for simultaneous selective redox transformation of organic aromatic compounds. The results indicate that the as-synthesized CdIn₂S₄ photocatalyst not only has excellent photocatalytic performance compared with pure In₂S₃ and CdS for the selective oxidation of aromatic alcohols in an oxygen environment, but also shows high photocatalytic redox activities under nitrogen atmosphere. A possible mechanism for the photocatalytic redox reaction in the coupled system was proposed. It is hoped that our current work could extend the applications of CdIn₂S₄ photocatalyst and provide new insights for selective transformations of organic compounds.

Hierarchical h-, m- and n-BiPO4 microspheres: facile synthesis and application in the photocatalytic decomposition of refractory phenols and benzene

Hierarchical structured n-BiPO₄ microspheres were prepared and exhibited excellent activity for photocatalytic degradation of bisphenol A, phenol, p-chlorophenol and benzene.

Enhanced photocatalytic removal of NO over titania/hydroxyapatite (TiO2/HAp) composites with improved adsorption and charge mobility ability

A 75% TiO₂/HAp composite photocatalyst with excellent NO removal efficiency was successfully synthesized. The photocatalytic improvement mechanism was investigated systematically.