Bi-based photocatalysts for bacterial inactivation in water: Inactivation mechanisms, challenges, and strategies to improve the photocatalytic activity

Double heterojunction photocatalysts: strategic fabrication and mechanistic insights towards sustainable fuel production

Excessive energy crisis has triggered the transformation of solar energy into chemical energy via photocatalysis to establish a sustainable and carbon-neutral society. In this regard, the fabrication of visible-light-active photocatalysts with favourable band edge positions is preferred for achieving maximum solar energy conversion efficiency. However, a single semiconductor suffers from several disadvantages, such as rapid electron-hole recombination, inefficient electron-hole separation and sluggish charge migration dynamics. To improve photocatalytic performance, constructing heterostructures using two semiconductors has been considered an effective strategy. Nonetheless, these binary heterostructures also present several challenges, which can be addressed by combining three semiconductors to form double heterojunctions. The formation of double heterojunctions enhances visible light absorption, increases charge carrier concentration and facilitates superior charge separation owing to the presence of in-built electric fields, thereby ameliorating the photocatalytic efficacy of these heterostructures compared to binary ones. This review article provides a deep insight into the charge transfer mechanisms that occur in different types of double heterojunctions. Moreover, it highlights the applications of these heterostructures in various fields of photocatalysis, such as water splitting, CO2 reduction, N2 fixation and pollutant degradation.

Bismuth-based photocatalysts for pollutant degradation and bacterial disinfection in sewage system: Classification, modification and mechanism

The discharge of polluted water poses a great threat to human health. Therefore, the development of effective sewage treatment technology is a key to achieve sustainable health development of society. Recent research showed that light-driven bismuth-based nanomaterials provided a promising chance for treating sewage system owing to their adjustable electronic features, excellent physical and chemical properties, abundant storage and environmental safety. However, the detailed overview and systematic understanding of the development of highly efficient bismuth-based photocatalysts is still unsatisfactory. In this review, we summarized the classification of bismuth-based photocatalysts, and the relationship between the structural design and the change of optical performance is illustrated. Importantly, the reliable modification strategies for improving photocatalytic capability are emphasized. Finally, the challenges and future development directions of light-driven bismuth-based nanoplatforms in wastewater treatment applications are discussed, hoping to provide an effective guidance for exploring the photocatalytic wastewater treatment process.

Laser Synthesis and Photocatalytic Properties of Bismuth Oxyhalides Nanoparticles

Photocatalysis offers a powerful approach for water purification from toxic organics, hydrogen production, biosolids processing, and the conversion of CO2 into useful products. Further advancements in photocatalytic technologies depend on the development of novel, highly efficient catalysts and optimized synthesis methods. This study aimed to develop a laser synthesis technique for bismuth oxyhalide nanoparticles (NPs) as efficient and multifunctional photocatalysts. Laser ablation of a Bi target in a solution containing halogen salt precursors, followed by laser plasma treatment of the resulting colloid, yielded crystalline bismuth oxyhalides (BixOyXz, where X = Cl, Br, or I) NPs without the need for additional annealing. The composition, structure, morphology, and optical properties of the synthesized BixOyXz (X = Cl, Br, I) NPs were characterized using XRD analysis, electron microscopy, Raman spectroscopy, and UV-Vis spectroscopy. The effect of the halogen on the photocatalytic activity of the double oxides was investigated. The materials exhibited high photocatalytic activity in the degradation of persistent model pollutants like Rhodamine B, tetracycline, and phenol. Furthermore, the BixOyXz NPs demonstrated good efficiency and high yield in the selective oxidation of 5-hydroxymethylfurfural (5-HMF) to 2,5-furandicarboxylic acid (FDCA). The obtained results highlight the promising potential of this laser synthesis approach for producing high-performance bismuth oxyhalide photocatalysts.

Recent Progress of Three-Dimensional Graphene-Based Composites for Photocatalysis

Converting solar energy into fuels/chemicals through photochemical approaches holds significant promise for addressing global energy demands. Currently, semiconductor photocatalysis combined with redox techniques has been intensively researched in pollutant degradation and secondary energy generation owing to its dual advantages of oxidizability and reducibility; however, challenges remain, particularly with improving conversion efficiency. Since graphene's initial introduction in 2004, three-dimensional (3D) graphene-based photocatalysts have garnered considerable attention due to their exceptional properties, such as their large specific surface area, abundant pore structure, diverse surface chemistry, adjustable band gap, and high electrical conductivity. Herein, this review provides an in-depth analysis of the commonly used photocatalysts based on 3D graphene, outlining their construction strategies and recent applications in photocatalytic degradation of organic pollutants, H2 evolution, and CO2 reduction. Additionally, the paper explores the multifaceted roles that 3D graphene plays in enhancing photocatalytic performance. By offering a comprehensive overview, we hope to highlight the potential of 3D graphene as an environmentally beneficial material and to inspire the development of more efficient, versatile graphene-based aerogel photocatalysts for future applications.

Perspectives for Photocatalytic Decomposition of Environmental Pollutants on Photoactive Particles of Soil Minerals

The literature shows that both in laboratory and in industrial conditions, the photocatalytic oxidation method copes quite well with degradation of most environmental toxins and pathogenic microorganisms. However, the effective utilization of photocatalytic processes for environmental decontamination and disinfection requires significant technological advancement in both the area of semiconductor material synthesis and its application. Here, we focused on the presence and "photocatalytic capability" of photocatalysts among soil minerals and their potential contributions to the environmental decontamination in vitro and in vivo. Reactions caused by sunlight on the soil surface are involved in its normal redox activity, taking part also in the soil decontamination. However, their importance for decontamination in vivo cannot be overstated, due to the diversity of soils on the Earth, which is caused by the environmental conditions, such as climate, parent material, relief, vegetation, etc. The sunlight-induced reactions are just a part of complicated soil chemistry processes dependent on a plethora of environmental determinates. The multiplicity of affecting factors, which we tried to sketch from the perspective of chemists and environmental scientists, makes us rather skeptical about the effectiveness of the photocatalytic decontamination in vivo. On the other hand, there is a huge potential of the soils as the alternative and probably cheaper source of useful photocatalytic materials of unique properties. In our opinion, establishing collaboration between experts from different disciplines is the most crucial opportunity, as well as a challenge, for the advancement of photocatalysis.

Recent progress on bismuth-based light-triggered antibacterial nanocomposites: Synthesis, characterization, optical properties and bactericidal applications

Bacterial infections pose a seriously threat to the safety of the environment and human health. In particular, the emergence of drug-resistant pathogens as a result of antibiotic abuse and high trauma risk has rendered conventional therapeutic techniques insufficient for treating infections by these so-called "superbugs". Therefore, there is an urgent need to develop highly efficient and environmentally-friendly antimicrobial agents. Bismuth-based nanomaterials with unique structures and physicochemical characteristics have attracted considerable attention as promising antimicrobial candidates, with many demonstratingoutstanding antibacterial effects upon being triggered by broad-spectrum light. These nanomaterials have also exhibited satisfactory energy band gaps and electronic density distribution with improved photonic properties for extensive and comprehensive applications after being modified through various engineering methods. This review summarizes the latest research progress made on bismuth-based nanomaterials with different morphologies, structures and compositions as well as the different methods used for their synthesis to meet their rapidly increasing demand, especially for antibacterial applications. Moreover, the future prospects and challenges regarding the application of these nanomaterials are discussed. The aim of this review is to stimulate interest in the development and experimental transformation of novel bismuth-based nanomaterials to expand the arsenal of effective antimicrobials.

Recent advances and new insights on the construction of photocatalytic systems for environmental disinfection

Photocatalysis, as a sustainable and environmentally friendly green technology, has garnered widespread recognition and application across various fields. Especially its potential in environmental disinfection has been highly valued by researchers. This study commences with foundational research on photocatalytic disinfection technology and provides a comprehensive overview of its current developmental status. It elucidates the complexity of the interface reaction mechanism between photocatalysts and microorganisms, providing valuable insights from the perspectives of materials and microorganisms. This study reviews the latest design and modification strategies (Build heterojunction, defect engineering, and heteroatom doping) for photocatalysts in environmental disinfection. Moreover, this study investigates the research focuses and links in constructing photocatalytic disinfection systems, including photochemical reactors, light sources, and material immobilization technologies. It studies the complex challenges and influencing factors generated by different environmental media during the disinfection process. Simultaneously, a comprehensive review extensively covers the research status of photocatalytic disinfection concerning bacteria, fungi, and viruses. It reveals the observable efficiency differences caused by the microstructure of microorganisms during photocatalytic reactions. Based on these influencing factors, the economy and effectiveness of photocatalytic disinfection systems are analyzed and discussed. Finally, this study summarizes the current application status of photocatalytic disinfection products. The challenges faced by the synthesis and application of future photocatalysts are proposed, and the future development in this field is discussed. The potential for research and innovation has been further emphasized, with the core on improving efficiency, reducing costs, and strengthening the practical application of photocatalysis in environmental disinfection.

Interfacial coupling of CuFe2O4 induced hotspots over self-assembled g-C3N4 nanosheets as an efficient photocatalytic bacterial disinfectant

Most bacterial disinfectants contain high levels of extremely toxic and environmental hazardous chemicals, which pose a significant threat to the ecosystem. Semiconductor photocatalysis exhibits attractive prospects as an emerging greener technology for waste water disinfection. However, the fast recombination of charge carriers limits its practical application. Herein, self-assembled polymeric feather-like g-C3N4 (GCN) nanosheets modified with ferromagnetic CuFe2O4 (CFO) nanospheres were successfully applied as a reusable visible light photocatalytic disinfectant. As expected, the g-C3N4/CuFe2O4 (GCF) nanohybrid displayed superior photocatalytic inactivation efficiency of 0.157log within 120 min towards Escherichia coli DH5α (E. coli) compared with pristine GCN and CFO. The characterization results revealed the synergistic heterostructure interfaces, high surface area, and the transformative self-assembly of GCN to feather-like structure providing a rich active site for improved charge separation efficiency, and wide spectral response, therefore the superior performance of GCF. The radical trapping assay proclaimed that both O2•- and •OH radical played major role in the photocatalytic inactivation among the other reactive oxygen species (ROS). Furthermore, the chemical oxygen demand (COD), protein estimation, and DNA estimation assay results validated the cell damage caused by the photocatalyst. Besides that, GCN showed applicability in real-time wastewater samples with improved efficiency than in the saline solution. The excellent magnetic characteristics facilitated the recycling of the catalyst with insignificant leaching, magnetic induction, and distinguished separation. The results of this work signify the well-designed GCF as a high-performance and reusable photocatalyst for real-world pathogenic bacterial disinfection operations.

Construction of floatable flower-like plasmonic Bi/BiOCl-loaded hollow kapok fiber photocatalyst for efficient degradation of RhB and antibiotics

The development of low-cost and high-efficiency photocatalysts for the degradation of organic pollutants has been an essential and feasible approach to environmental remediation. However, conventional powder photocatalysts suffer from agglomeration, limited light utilization, and reuse difficulties, which hinder their large-scale practical application. Herein, a floatable flower-like plasmonic Bi/BiOCl-loaded hollow kapok fiber (KF/Bi/BC) photocatalyst was synthesized by a facile solvothermal method. It exhibited excellent photocatalytic degradation of Rhodamine B (RhB), ofloxacin (OFX), and tetracycline (TC) under UV-vis irradiation. The incorporation of metallic Bi not only greatly enhanced the light absorption of BiOCl in the visible region but also served as an effective "electron trap", facilitating the efficient separation and transfer of photogenerated electrons and holes. Furthermore, the remarkable floatability of the catalyst contributed to increased light utilization and facilitated the recycling of the catalyst. This work provided a convenient, effective, and feasible method for the fabrication of floatable photocatalysts with excellent catalytic properties, and has great potential for practical applications.

Ag Nanoparticle and Ti-MOF Cooperativity for Efficient Inactivation of E. coli in Water

Because of the limitations of traditional chlorine-based bactericidal water treatment, such as the formation of disinfection byproducts (DBPs) and resistance to chlorine, novel approaches and materials are required for effective disinfection of water. This study focuses on the development of a new sterilization material, Ag/NH2-MIL-125(Ti), which was designed to effectively inactivate Escherichia coli in water. The effectiveness of the as-designed material stems from the synergistic interactions between Ag nanoparticles (NPs) and photoactive metal-organic frameworks (MOFs). In this complex material, the MOFs play a critical role in dispersing and isolating the Ag NPs, thus preventing undesirable aggregation during bacterial inactivation. Simultaneously, Ag NPs enhance the photocatalytic performance of the MOFs. Sterilization experiments demonstrate the remarkable rapid E. coli inactivation performance of Ag/NH2-MIL-125(Ti) under illuminated and nonilluminated conditions. Within 25 min of visible light exposure, the as-prepared material achieves a >7-log E. coli reduction. In addition, Ag/NH2-MIL-125(Ti) efficiently decomposes acetic acid, which is the main DBP precursor, under visible light irradiation. Mechanistic investigations revealed that •O2- and h+ were the primary active substances responsible for the inactivation of E. coli and the decomposition of acetic acid, respectively.

Synergetic effect of CQD and oxygen vacancy to TiO2 photocatalyst for boosting visible photocatalytic NO removal

The wide band gap of TiO₂ photocatalyst material limits its application in the field of visible photocatalysis. In this paper, oxygen vacancies and carbon quantum dots (CQD) with up-conversion character were proposed to improve the photocatalytic activity for NO removal of TiO₂ under visible light irradiation. The one-dimensional TiO₂ nanotube (TNs), TNs containing oxygen vacancies (OVTNs), TNs of composite CQD (CQD-TNs) and OVTNs of composite CQD (CQD-OVTNs) were prepared, respectively. Furthermore, the influence of oxygen vacancies and CQD on the removal of NOx by photocatalysis were explored. It is found that CQD-OVTNs exhibits the conspicuous synergetic effect of CQD and oxygen vacancy to boost visible photocatalytic NO removal, the NO removal efficiency was about 12, 2, and 2.6 times to TNs, OVTNs and CQD-TNs. Also, CQD-OVTNs exhibits the NO₂-inhibited property during the process of photocatalytic NO removal. Finally, the synergetic mechanism of CQD and oxygen vacancies to TNs for boosting visible photocatalytic NO removal was revealed.

Biomimetic Guided Bi2WO6/Bi2O3 Vertical Heterojunction with Controllable Microstructure for Efficient Photocatalysis

To bridge the technical gap of heterojunction induction control in conventional semiconductor photocatalysts, a method of regulating the growth of heterojunctions utilizing biomimetic structures was designed to prepare a series of Bi2WO6/Bi2O3 vertical heterojunction nanocomposites for the disposal of environmentally hazardous tetracycline wastewater difficult to degrade by conventional microbial techniques. Porous Bi2O3 precursors with high-energy crystalline (110) dominant growth were produced using the sunflower straw bio-template technique (SSBT). Bi2WO6 with a (131) plane grew preferentially into 2.8 to 4 nm pieces on the (110) plane of Bi2O3, causing a significant density reduction between Bi2WO6 pieces and a dimensional decrease in the agglomerated Bi2WO6 spheres from 3 μm to 700 nm since Bi2WO6 grew on the structure of the biomimetic Bi2O3. The optimal 1:8 Bi2WO6/Bi2O3 coupling catalyst was obtained via adapting the ratio of the two semiconductors, and the coupling ratio of 1:8 minimized the adverse effects of the overgrowth of Bi2WO6 on degradation performance by securing the quantity of vertical heterojunctions. The material degradation reaction energy barrier and bandgap were significantly reduced by the presence of a large number of vertical heterojunction structures, resulting in a material with lower impedance and higher electron–hole separation efficiency; thus, the degradation efficiency of 1:8 Bi2WO6/Bi2O3 for tetracycline hydrochloride reached 99% within 60 min. In conclusion, this study not only successfully synthesized a novel photocatalyst with potential applications in water pollution remediation but also introduced a pioneering approach for semiconductor-driven synthesis.

Understanding the Principles and Applications of Dual Z-Scheme Heterojunctions: How Far Can We Go?

In the past seven years, dual Z-scheme heterojunctions evolved as favorable approaches for enhanced charge carrier separation through direct or indirect charge transfer transportation mechanisms. The dynamics of the charge transfer is the major strategy for understanding their photoactivity and stability through the formation of distinctive redox centers. The understanding of currently recognized principles for successful fabrication and classification in different energy and pollution remediation strategies is discussed, and a universal charge transfer-type-based classification of dual Z-schemes that can be adopted for Z-scheme and S-scheme heterojunctions is proposed. Methods used for determining the charge transfer as proof of dual Z-scheme existence are outlined. Most importantly, a new macroscopic N-scheme and a triple Z-scheme that can also be adopted as triple S-scheme heterostructures composed of four semiconductors are proposed for generating both oxidatively and reductively empowered systems. The proposed systems are expected to possess properties that enable them to harvest solar light to drive important chemical reactions for different applications.

Novel La3+/Sm3+ co-doped Bi5O7I with efficient visible-light photocatalytic activity for advanced treatment of wastewater: Internal mechanism, TC degradation pathway, and toxicity analysis

Controlling semiconductor photocatalysts by doping rare-earth ions is an effective strategy to improve photocatalytic performance. Simple solvothermal and calcination methods were used to prepare La³⁺ and Sm³⁺ modified Bi₅O₇I nanomaterials. Some characterizations such as XRD, XPS, SEM, TEM, UV-vis, etc. were carried out to explore its structural composition and photoelectrochemical properties. The photocatalytic activity was investigated by simulating the degradation of TC and RhB under visible-light irradiation. The degradation results showed that the photocatalytic efficiency of 4S4L-Bi₅O₇I was the best among the samples with the 100% degradation rate of TC (Tetracycline hydrochloride) and 93% of RhB (Rhodamine B). The capture experiment and ESR test proved that the active substances that play a role in the photocatalytic degradation of pollutants were ·O₂^-, ¹O₂ and h⁺, and on this basis, the possible degradation mechanism was proposed. The final results showed that La/Sm co-doping expanded the light absorption range of Bi₅O₇I and improved the charge separation efficiency and the specific surface area. Besides, the surface defects were formed on the surface of Bi₅O₇I due to ion-doping, which could catch e^- to promote the separation and transfer of carriers and improve the photocatalytic activity. LC-MS was used to analyze the possible degradation pathways of TC. And the toxicity of TC was also analyzed via T.E.S.T and Toxtree. The results showed comprehensive toxicity of TC was decreased by 4S4L-Bi₅O₇I so that the overall water pollution was reduced. This work can provide a reference for the subsequent development of bismuth-based photocatalysts.

Preparation of a Bi6O5(OH)3(NO3)5·2H2O/AgBr composite and its long-lasting antibacterial efficacy

A novel Bi6O5(OH)3(NO3)5·2H2O/AgBr (6535BBN/AgBr) composite with long-lasting antibacterial efficacy was prepared. The microstructure of the composite was characterized. AgBr nanoparticles (NPs) were sandwiched in 6535BBN nanosheets (NSs) or loaded on their surfaces. The utilization of 6535BBN as carriers contributed to the long-term lasting antibacterial activity of the composite after storage in water or 0.9% NaCl. The antibacterial activity was evaluated by inhibition zones against E. coli. The inhibition zone diameters of 6535BBN/AgBr stored in water for 0 h, 8 h, 16 h, and 48 h were measured as 22.50, 21.71, 20.43, and 20.29 mm, respectively. The activity of the composite after storage in water for 48 h remained 90.2% of that in the beginning. After storing in 0.9% NaCl for 16 h, the activity was determined to be 90.1% of that in the beginning. In comparison with the rapid decrease in the antibacterial activity of pure AgBr, the slow reduction of 6535BBN/AgBr after storage indicates long-lasting efficacy. The excellent dispersion states of 6535BBN/AgBr powders after storage in solutions were revealed, and the positive relationship between the dispersion state and its long-lasting antibacterial activity was suggested. Based on the unique load-on-carrier (LOC) structure, the long-lasting antibacterial performance was promoted by the synergy of the sharp-edge-cutting effect of 6535BBN NSs, prolonged ROS antibacterial effect, and restrained sterilization effects of silver ions caused by their slow release.

Complete and simultaneous removal of ionic silver and silver nanoparticles by using an ionic liquid supported on a magnetic nanoparticle core

The global pandemic situation due to COVID-19 has given rise to the massive use of disinfectant products, many of them based on silver atoms. After the use of these products, the silver passes into the aqueous effluents, becoming an emerging contaminant in waters. In this work, a novel procedure for the total and simultaneous removal of ionic and nanomeric silver in aqueous samples is introduced, employing magnetic nanoparticles wrapped with an ionic liquid (Fe₃O₄@IL) as a removal agent. Experimental variables such as pH, contact time, temperature, as well as pollutant and removal agent doses were studied to achieve the total elimination, exhibiting exceptional conditions for the removal of different concentrations of silvers species in water. The approach achieves 100% removal efficiency for the simultaneous removal of both silver species, goal not achieved previously. Also, 100% removal efficiency is reached for the both species separately, since ionic silver is adsorbed onto the Fe₃O₄, while nanomeric silver is extracted in the IL. Particularly, for concentrations within the range 50-200 μg L^-1, total removal efficiency was reached for a wide range of temperatures and a pH range 7-9, achieved in just 15 min, for all cases. Additionally, the doses of Fe₃O₄@IL employed to remove all concentrations of silver were 13.7 mg. Characterization of Fe₃O₄@IL surfaces before and after the process was performed by means of Field Effect Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy. Fe₃O₄@IL was recycled by employing 100 μL of 1% HNO₃ solution, allowing its use for 10 additional silver removal cycles without loss of efficiency. The study of adsorption kinetics and equilibrium isotherms reveal a Freundlich-type adsorption, which suggests affinity between sites in the complex surface of Fe₃O₄@IL, and Elovich kinetics, indicative of chemisorption onto a heterogeneous surface, while the temperature shows no effect on the results.