Designing and modification of bismuth oxyhalides BiOX (X = Cl, Br and I) photocatalysts for improved photocatalytic performance

Investigation into the Performance and Mechanism of BiOX Photocatalytic Degradation of Toluene under Sunlight

The existence of indoor volatile organic compound pollution cannot be ignored. The main representative pollutant, toluene, poses a serious danger to human health. In this study, BiOX (X = Cl, Br, I) nanophotocatalytic materials were synthesized using a straightforward chemical precipitation process. The materials' fundamental structure and characteristics were examined, and it was investigated whether they can remove toluene gas pollutants when put them under sunlight. According to the results, within 120 min, the degradation rates of toluene are ranked as BiOCl > BiOI > BiOBr, with BiOBr achieving 16.16%, BiOI 28.13%, and BiOCl exhibiting the highest degradation efficiency at approximately 56.41%. Toluene was entirely broken down with fewer intermediates, according to the conversion rate of CO2, the degradation product. There was also extensive research on the photocatalytic mechanism of BiOCl under sunlight. The π-bonds within the toluene benzene ring were broken by the active radicals •OH and •O2 -. Furthermore, the oxygen vacancies and the holes (h+) worked in concert to enhance the toluene molecule's adsorption and activation, which accelerated the breakdown of toluene into short-chain molecules, and it became carbon dioxide and water, eventually. These reactions were considered to be environmentally and friendly. The study gives a practical way to lessen indoor VOC pollution and theoretical evidence for BiOCl photocatalytic degradation of toluene gas.

Engineered oxygen vacancies in NiCo2O4/BiOI heterostructures for enhanced photocatalytic pollutant degradation

To address the bottleneck issue of poor carrier separation and transfer efficiency in NiCo2O4 photocatalyst, a novel 1D/2D-rod-on-rose-like NiCO2O4/BiOI nanohybrid with abundant OV's was successfully synthesized using a single-step hydrothermal method and employed to the photocatalytic degradation of Rhodamine B (RhB). The study revealed that the optimized NiCo2O4-OV/BiOI hybrid could possess superior photocatalytic degradation efficiency towards RhB degradation under visible light with a rate constant that was 3.8 and 3.03 times greater than that of BiOI and NiCo2O4-OV. Experimental findings indicated that the formation of NiCo2CO4-OV/BiOI heterojunction significantly improved the charge separation efficiency and facilitated the formation of surface OV's. These OVs enhanced photogenerated e--h+ separation and increased catalytic efficiency. Quenching experiments results confirmed that both holes and superoxide radicals are playing crucial roles in the degradation process. Thus, an oxygen vacancy and engineering NiCo2CO4-OV/BiOI heterojunction-enhanced degradation mechanism was proposed, offering insights for the integration of advanced oxidation technologies and the development of catalytic materials to enhance pollutant degradation efficiency.

Modulating Surface-Adsorbed Oxygen Species of Bismuth Silicate by a Solid Solution Strategy for Efficient Adsorption and Photocatalytic Activity

Bismuth silicate photocatalysts suffer from insufficient photocatalytic activity due to an insufficient number of surface active sites and low carrier separation and transport efficiency, which can be solved by defect modulation. Herein, Bi12SiO20/Bi2O2SiO3-BiOClxBr1-x (BSOCB) photocatalysts with a high concentration of surface-adsorbed oxygen species (SAOS) are synthesized by introducing a BiOClxBr1-x solid solution to modify nonhomogeneous BSO via an ion exchange strategy. The introduction of a solid solution enables the generation of dispersed nanoflowers and the regulation of SAOS due to the fact that anion-cation copolymerization guides the crystal growth, and the defects generated by the lattice distortion modulate the concentration of SAOS on the catalysts during the solid solution process. The obtained typical BSOCB photocatalyst possesses both high adsorption and photocatalytic properties, and the results show that it not only can almost completely degrade the traditional pollutant RhB within 20 min but also strongly degrades antibiotics, such as CIP (light for 150 min, 96%), NFX (light for 150 min, 87%), and TC (light for 150 min, 77%). This work provides a new approach for obtaining bismuth-based photocatalysts with controllable morphology and a large number of surface active sites and provides a theoretical and experimental basis for expanding the application scenarios of photocatalysts.

Sn-based materials in photocatalysis: A review

Development and the application of Sn-based materials have become more prevalent in recent years due to concerns regarding the energy crisis, environmental pollution, and the urgent need of constructing inexpensive and highly effective photocatalysis. The recent advancement in Sn-based materials for efficient photocatalysts, such as Sn alloys, Sn oxides, Sn sulfides, Sn selenides, Sn niobates, Sn tantalites, and Sn tungstates, is summarized in this study. Several design ideas for increasing the photoactivity of Sn-based materials in various photocatalytic applications are emphasized. In addition, we considered their present applications in energy generation (H2 evolution, CO2 reduction, and N2 fixation) and environmental remediation (air purification and wastewater treatment). As a result, the current review will deepen the reader's understanding of the properties and potential uses of Sn-based materials in photocatalysis. Hence, this paper will serve as a guide in promoting the domain of Sn-based materials for future photocatalytic technologies.

Visible light induced degradation of perfluorooctanoic acid using iodine deficient bismuth oxyiodide photocatalyst

A bismuth oxyiodide photocatalyst having coexistent iodine deficient phases viz. Bi₄O₅I₂ and Bi₅O₇I was prepared by using a solvothermal method followed by calcination process. This has been used for the degradation of model perfluoroalkyl acids such as perfluorooctanoic acid at low concentrations (1 ppm) under simulated solar light irradiation. 94% PFOA degradation with a rate constant of 1.7 h^-1 and 65% defluorination of PFOA have been achieved following 2 h of photocatalysis. The degradation of PFOA happened by the parallel direct redox reactions with high energy photoexcited electrons at the conduction band, electrons in iodine vacancies and superoxide radicals. The degradation intermediates were analyzed by electrospray ionization-mass spectrometry in the negative mode. The catalyst was converted to a more iodine deficient Bi₅O₇I phase during photocatalysis following creation of iodine vacancies, some of which were compensated by the fluoride ions released from degraded PFOA.

Applications of BiOX in the Photocatalytic Reactions

BiOX (X = Cl, Br, I) families are a kind of new type of photocatalysts, which have attracted the attention of more and more researchers. The suitable band gaps and their convenient tunability via the change of X elements enable BiOX to adapt to many photocatalytic reactions. In addition, because of their characteristics of the unique layered structure and indirect bandgap semiconductor, BiOX exhibits excellent separation efficiency of photogenerated electrons and holes. Therefore, BiOX could usually demonstrate fine activity in many photocatalytic reactions. In this review, we will present the various applications and modification strategies of BiOX in photocatalytic reactions. Finally, based on a good understanding of the above issues, we will propose the future directions and feasibilities of the reasonable design of modification strategies of BiOX to obtain better photocatalytic activity toward various photocatalytic applications.

A Cu medium designed Z-scheme ZnO-Cu-CdS heterojunction photocatalyst for stable and excellent H2 evolution, methylene blue degradation, and CO2 reduction

Solar photocatalysis has emerged as a pollution-free and inexhaustible technique that has been extensively researched in the domains of environmental remediation and energy production. Herein, we have integrated ZnO and CdS nanoparticles through Cu as a solid-state electron mediator to design a ZnO-Cu-CdS Z-scheme heterosystem via a sol-gel route and further tested this as a photocatalyst for dye degradation, H₂ evolution, and CO₂ reduction. Within 60 min of visible light exposure, about 97% of methylene blue (MB) is degraded with a degradation rate constant of 0.042 min^-1 for the ZnO_0.45Cu_0.1CdS_0.45 catalyst. The MB degradation with this catalyst is 84, 21, 4.8, and 2 times as high as those of ZnO, CdS, ZnO_0.5CdS_0.5, and Cu_0.1ZnO_0.9 catalysts. The ZnO-Cu-CdS catalyst manifests an H₂ evolution efficiency of 5579 μmol h^-1 g^-1, which is 169, 41, 3.9, and 3.5 times as high as those of ZnO, CdS, ZnO_0.5CdS_0.5, and Cu_0.1ZnO_0.9 catalysts. Using H₂ as a reducing agent, the CO production rate over the ZnO_0.45Cu_0.1CdS_0.45 catalyst reaches 770 μmol h^-1 g^-1, which is 3 and 1.8 times higher than those of ZnO_0.5CdS_0.5 and Cu_0.1ZnO_0.9 catalysts. Besides, the optimal CH₄ production rate over ZnO_0.45Cu_0.1CdS_0.45 reaches 890 μmol h^-1 g^-1. The improved photocatalytic response of the ZnO-Cu-CdS catalyst is assigned to the delayed recombination of photoexcited charge carriers through a Z-scheme charge transport mode, maintaining the photocarriers with strong redox potentials and the dual role of Cu to serve as a conductive bridge to accelerate the charge transfer rate and enhance the light absorption due to its SPR phenomenon. This research offers a promising strategy for developing binary/ternary Z-scheme heterojunction photocatalytic systems for different photocatalytic applications.

Recent advances in Metal Organic Framework (MOF)-based hierarchical composites for water treatment by adsorptional photocatalysis: A review

Architecting a desirable and highly efficient nanocomposite for applications like adsorption, catalysis, etc. has always been a challenge. Metal Organic Framework (MOF)-based hierarchical composite has perceived popularity as an advanced adsorbent and catalyst. Hierarchically structured MOF material can be modulated to allow the surface interaction (external or internal) of MOF with the molecules of interest. They are well endowed with tunable functionality, high porosity, and increased surface area epitomizing mass transfer and mechanical stability of the fabricated nanostructure. Additionally, the anticipated optimization of nanocomposite can only be acquired by a thorough understanding of the synthesis techniques. This review starts with a brief introduction to MOF and the requirement for advanced nanocomposites after the setback faced by conventional MOF structures. Further, we discussed the background of MOF-based hierarchical composites followed by synthetic techniques including chemical and thermal treatment. It is important to rationally validate the successful nanocomposite fabrication by characterization techniques, an overview of challenges, and future perspectives associated with MOF-based hierarchically structured nanocomposite.

Facile construction of photocatalytic cellulose-based sponge with stable flotation properties as efficient and recyclable photocatalysts for sewage treatment

Dispersion and recycling of powdered nano-photocatalysts for water purification is still not an easy task. The self-supporting and floating photocatalytic cellulose-based sponges ware conveniently prepared by anchoring BiOX nanosheet arrays on cellulose-based sponge's surface. The introduction of sodium alginate into the cellulose-based sponge significantly enhanced the electrostatic adsorption of bismuth oxygen ions and promoted the formation of bismuth oxyhalide (BiOX) crystal nuclei. Among the photocatalytic cellulose-based sponges, the sponge (BiOBr-SA/CNF) modified with bismuth oxybromide displayed excellent photocatalytic ability for photodegrading 96.1 % rhodamine B within 90 min under 300 W Xe lamp irradiation (λ > 400 nm). The loading of bismuth oxybromide on cellulose-based sponge's surface improves the flotation stability of the cellulose-based sponge. Benefiting from excellent load fastness of bismuth oxybromide nanosheet and flotation stability of BiOBr-SA/CNF sponge, after 5 cycles of recycling, the photodegradation rates of BiOBr-SA/CNF sponge to rhodamine B remained above 90.2 % (90 min), and it also has excellent photocatalytic degradation effect on methyl orange and herbicide isoproteron. This work may provide a convenient and efficient method to construct self-supporting and floating photocatalytic sponges using cellulose based materials as substrates for sewage treatment.

Effects of high pressure on the lattice structure and electrical transport properties of BiOI

To reveal the pressure effects on BiOX semiconductors, we performed in-situ Raman spectroscopy and electrical transport measurements on BiOI up to 26.1 GPa and 19.2 GPa. BiOI showed good structural stability, while the electron conduction characteristics maintained dominance throughout the pressure range. The influence of grain boundary conduction disappeared at pressures above 9.2 GPa. With pressure elevation, the pressure-induced lattice fragmentation and grain refinement introduced a large number of relevant levels in the energy gap and resulted in a significant increase in the conductivity of BiOI under compression. The conductivity increased by 10⁶ at 19.2 GPa from the initial value and maintained an increase of 10² after depressurization until ambient conditions were attained. At the same time, the space charge polarization of the crystal interface layer became weaker with pressure elevation resulting in a decrease in the relative permittivity of BiOI. The calculation results of the complex permittivity showed that the frequency of orientation polarization response decreases with pressure elevation, and the complex permittivity becomes constant in the high-frequency region. Our work proves that pressure could significantly increase the carrier concentration and mobility, thus effectively improving the conductivity of BiOX semiconductors.

Facile synthesis CQDs/SnO2-x/BiOI heterojunction photocatalyst to effectively degrade pollutants and antibacterial under LED light

To remove multitudinous pollutants from wastewater, the design of a highly efficient and multifunctional photocatalyst is necessary. A novel CQDs/SnO2-x/BiOI photocatalyst (named CSnBI composite) was prepared by combining carbon quantum dots (CQDs), large specific surface area SnO2-x nanocrystals and BiOI nanocrystals to obtain a compact hybrid structure. TEM and Raman techniques confirmed the structure of CSnBI composite. The photocurrent and EIS showed that the photoexcited electron-hole pairs separation efficiency was improved. As anticipated, novel CSnBI photocatalyst can successfully remove tetracycline, methyl orange, E. coli (Escherichia coli) and S. aureus under a LED light due to the hybridization contaction among CQDs, SnO2-x and BiOI. The mechanism showed that the introduction of CQDs promoted visible light absorption and efficient separation of photogenerated carriers of SnO2-x/BiOI heterojunction. The capture experiment and related measurements showed that h+, •O2- and •OH are active species in the photocatalytic process. This study gave a novel case for facile construction of photocatalysts with tight hybrid structure.

Role of p-n junction initiated mixed-dimensional 0D/2D, 1D/2D, and 2D/2D BiOX (X = Cl, Br, and I)/TiO2 nanocomposite interfaces for environmental remediation applications: A review

Nowadays, we are critically facing various environmental issues. Among these, water contamination is the foremost issue, which worsens our health and living organisms in the water. Thus, it is necessary to provide an avenue to minimize the toxic matter through the development of facile technique and harmless photocatalyst. In this review, we intended to uncover the findings associated with various 0D, 1D, and 2D nanostructures featured photocatalysts for advancements in interfacial characteristics and toxic matter degradation. In this context, we evaluated the promising mixed-dimensional 0D/2D, 1D/2D, and 2D/2D bismuth oxyhalides BiOX (X = Cl, Br, and I) integrated TiO₂ nanostructure interfaces. Tunable mixed-dimensional interfaces highlighted with higher surface area, more heterojunctions, variation in the conduction and valence band potential, narrowed band gap, and built-in electric field formation between BiOX and TiO₂, which exhibits remarkable toxic dye, heavy metals, and antibiotics degradation. Further, this review further examines insights into the charge carrier generation, separation, and shortened charge transfer path at reduced recombination. Considering the advantages of type-II, S-scheme, and Z-scheme charge transfer mechanisms in the BiOX/TiO₂, we heightened the combination of various reactive species generation. In a word, the concept of mixed-dimensional BiOX/TiO₂ heterojunction interface endows toxic matter adsorption and decomposition into useful products. Challenges and future perspectives are also provided.

Bismuth Oxyhalide-Based Materials (BiOX: X = Cl, Br, I) and Their Application in Photoelectrocatalytic Degradation of Organic Pollutants in Water: A Review

An important target of photoelectrocatalysis (PEC) technology is the development of semiconductor-based photoelectrodes capable of absorbing solar energy (visible light) and promoting oxidation and reduction reactions. Bismuth oxyhalide-based materials BiOX (X = Cl, Br, and I) meet these requirements. Their crystalline structure, optical and electronic properties, and photocatalytic activity under visible light mean that these materials can be coupled to other semiconductors to develop novel heterostructures for photoelectrochemical degradation systems. This review provides a general overview of controlled BiOX powder synthesis methods, and discusses the optical and structural features of BiOX-based materials, focusing on heterojunction photoanodes. In addition, it summarizes the most recent applications in this field, particularly photoelectrochemical performance, experimental conditions and degradation efficiencies reported for some organic pollutants (e.g., pharmaceuticals, organic dyes, phenolic derivatives, etc.). Finally, as this review seeks to serve as a guide for the characteristics and various properties of these interesting semiconductors, it discusses future PEC-related challenges to explore.

Oxygen vacancy engineering of novel ultrathin Bi12O17Br2 nanosheets for boosting photocatalytic N2 reduction

The conversion of N₂ to NH₃ is one of the most promising processes in maintaining natural life and chemical production. Photocatalytic nitrogen reduction reaction (NRR) has the advantage of clean and sustainable, which is considered to be an ideal synthesis technology. In this work, we report the successful synthesis of Bi₁₂O₁₇Br₂ ultrathin nanosheets through simple alkali treatment and solvothermal method. The Bi₁₂O₁₇Br₂ ultrathin nanosheets can improve the separation of carriers and the transfer of photogenerated electrons to N₂ molecules, thus improving the photocatalytic efficiency. Of note, the higher Bi/Br atomic ratio in Bi₁₂O₁₇Br₂ is beneficial to broaden the light absorption edge, and the high concentration of O atoms is easy to produce oxygen vacancies on the surface during the synthesis process of Bi₁₂O₁₇Br₂. The abundant oxygen vacancies and high specific surface area enable N₂ molecules and water to have powerful chemical adsorption and activation. In addition, the photocatalytic reduction of N₂ to NH₃ in pure water shows excellent and stable performance, and the average generation rate of NH₃ reaches up to 620.5 μmol·L^-1·h^-1. This study discovers that rich oxygen vacancies and ultrathin morphology may have a significant part in the process of the photocatalytic nitrogen reduction reaction.