Mechanism and experimental study on the photocatalytic performance of Ag/AgCl @ chiral TiO2 nanofibers photocatalyst: the impact of wastewater components

Chiral Inorganic Nanomaterials for Photo(electro)catalytic Conversion

Chiral inorganic nanomaterials due to their unique asymmetric nanostructures have gradually demonstrated intriguing chirality-dependent performance in photo(electro)catalytic conversion, such as water splitting. However, understanding the correlation between chiral inorganic characteristics and the photo(electro)catalytic process remains challenging. In this perspective, we first highlight the chirality source of inorganic nanomaterials and briefly introduce photo(electro)catalysis systems. Then, we delve into an in-depth discussion of chiral effects exerted by chiral nanostructures and their photo-electrochemistry properties, while emphasizing the emerging chiral inorganic nanomaterials for photo(electro)catalytic conversion. Finally, the challenges and opportunities of chiral inorganic nanomaterials for photo(electro)catalytic conversion are prospected. This perspective provides a comprehensive overview of chiral inorganic nanomaterials and their potential in photo(electro)catalytic conversion, which is beneficial for further research in this area.

Influence of wastewater matrix on the visible light degradation of phenol using AgCl/Bi24O31Cl10 photocatalyst

A significant amount of research has been conducted on the development and application of photocatalytic materials for the visible light degradation of organic pollutants in wastewater. However, most pollutant degradation studies are conducted using simulated wastewater often prepared using DI water. This is far removed from the realities of environmentally relevant water systems. It is therefore important to investigate the activity of these semiconductor materials with real water samples. In this study, the photocatalytic activity of the photocatalyst was investigated in the secondary effluent of a wastewater treatment plant (WWTP) in Pretoria, South Africa, for the degradation of phenol under visible light irradiation. The experimental design was done using the Taguchi method L16 orthogonal tray with three factors (pH, initial phenol concentration, and photocatalyst dosage) and four levels. The results show that pH is the highest-ranked significant factor influencing the degradation rate, closely followed by the initial concentration of the pollutant. The photocatalyst dosage had the least significant impact on degradation. The effects of individual anion components such as Cl-, NO3-, NO2-, SO42- and cations such as Ca2+, Mg2+, Zn2+, and K+ were investigated. While Cl- did not negatively influence the degradation rate, the results show that NO3- and SO42- inhibit the degradation of phenol. More specifically, the presence of nitrites resulted in total impeding of the degradation process illustrating that nitrite concentrations ≥ 20 ppm should be removed from wastewater prior to photocatalytic degradation. The cations investigated promoted the degradation of phenol. Generally, there was enhanced degradation in the water matrix when compared to DI water, and the results revealed improved degradation efficiency due to the cumulative impact of various components of the wastewater.

Synthesis and application of titanium dioxide photocatalysis for energy, decontamination and viral disinfection: a review

Global pollution is calling for advanced methods to remove contaminants from water and wastewater, such as TiO₂-assisted photocatalysis.  The environmental applications of titanium dioxide have started after the initial TiO₂ application for water splitting by Fujishima and Honda in 1972. TiO₂ is now used for self-cleaning surfaces, air and water purification systems, microbial inactivation and selective organic conversion. The synthesis of titanium dioxide nanomaterials with high photocatalytic activity is actually a major challenge. Here we review titanium dioxide photocatalysis with focus on mechanims, synthesis, and applications. Synthetic methods include sol-gel, sonochemical, microwave, oxidation, deposition, hydro/solvothermal, and biological techniques. Applications comprise the production of energy, petroleum recovery, and the removal of microplastics, pharmaceuticals, metals, dyes, pesticides, and of viruses such as the severe acute respiratory syndrome coronavirus 2.

Silver Halide-Based Nanomaterials in Biomedical Applications and Biosensing Diagnostics

In recent years, silver halide (AgX, X = Cl, Br, I)-based photocatalytic materials have received increasing research attention owing to their excellent visible-light-driven photocatalytic performance for applications in organic pollutant degradation, HER, OER, and biomedical engineering. Ag as a noble metal has a surface plasma effect and can form Schottky junctions with AgX, which significantly promotes electron transport and increases photocatalytic efficiency. Therefore, Ag/AgX can reduce the recombination rate of electrons and holes more than pure AgX, leading to using AgX as a photocatalytic material in biomedical applications. The use of AgX-based materials in photocatalytic fields can be classified into three categories: AgX (Ag/AgX), AgX composites, and supported AgX materials. In this review, we introduce recent developments made in biomedical applications and biosensing diagnostics of AgX (Ag/AgX) photocatalytic materials. In addition, this review also discusses the photocatalytic mechanism and applications of AgX (Ag/AgX) and supported AgX materials.

Intimately coupled gC3N4 photocatalysis and mixed culture biofilm enhanced detoxification of sulfamethoxazole: Elucidating degradation mechanism and toxicity assessment

In recent years, wide spread of antibiotic-resistant microorganisms and genes emerging globally, an eco-friendly method for efficient degradation of antibiotics from the polluted environment is essential. Intimately coupled photocatalysis and biodegradation (ICPB) using gC₃N₄ for enhanced degradation of sulfamethoxazole (SMX) was investigated. The gC₃N₄ were prepared and coated on the carbon felt. The mixed culture biofilm was developed on the surface as a biocarrier. The photocatalytic degradation showed 74%, and ICPB exhibited 95% SMX degradation efficiency. ICPB showed superior visible light adsorption, photocatalytic activity, and reduced charge recombination. The electron paramagnetic resonance spectrum confirms that the generation of •OH and O₂• radicals actively participated in the degradation of SMX into biodegradable intermediated compounds, and then, the bacterial communities present in the biofilm mineralized the biodegradable compound into carbon dioxide and water. Moreover, the addition of NO₃^-, PO₄^-, and Cl^- significantly enhanced the degradation efficiency by trapping the surface electron. Stability experiments confirmed that gC₃N₄ biohybrid can maintain 85% SMX degradation efficiency after 5 consecutive recycling. Extracellular polymeric substances characterization results show that biohybrid contains 47 mg/L, 14 mg/L, and 13 mg/L protein, carbohydrate, and humic acid, respectively, which can protect the bacterial communities from the antibiotic toxicity and reactive oxygen species. Furthermore, biotoxicity was investigated using degradation products on E.coli and results revealed 83% detoxification efficiency. Overall, this study suggested that gC₃N₄ photocatalyst in an ICPB can be used as a promising eco-friendly method to degrade sulfamethoxazole efficiently.

Degradation of Minocycline by the Adsorption-Catalysis Multifunctional PVDF-PVP-TiO2 Membrane: Degradation Kinetics, Photocatalytic Efficiency, and Toxicity of Products

The photocatalytic degradation of minocycline was studied by using polyvinylidene fluoride-polyvinylpyrrolidone-TiO₂ (PVDF-PVP-TiO₂) fiber mats prepared by an electrospinning technology. The influences of the TiO₂ dosage, minocycline concentrations, inorganic anions, pH values, and dissolved organic matter (DOM) concentrations on the degradation kinetics were investigated. A mass of 97% minocycline was degraded in 45 min at 5% TiO₂ dosage. The corresponding decomposition rate constant was 0.069 min^-1. The inorganic anions affected the minocycline decomposition in the order of HCO₃^- > Cl^- > SO₄^2- > NO₃^-, which was confirmed by the results of electron spin resonance (ESR) spectra. The lowest electrical energy per order (E_EO) was 6.5 Wh/L. Over five cycles, there was no change in the photocatalytic performance of the degrading minocycline. Those investigations suggested that effective degradation of minocycline could be reached in the PVDF-PVP-TiO₂ fiber mats with a low energy consumption, good separation and, good recovery. Three photocatalytic decomposition pathways of minocycline were proposed: (i) hydroxyl substitution of the acylamino group; (ii) hydroxyl substitution of the amide group, and (iii) a cleavage of the methyl groups and further oxidation of the amino group by OH. Potential risks caused by TP159 and TP99 should not be ignored, while the TP90 are nontoxic. Tests indicated that the toxicity of the photocatalytic process may be persistent if minocycline and its products were not mineralized completely.

Engineering and modeling perspectives on photocatalytic reactors for water treatment

The debate on whether photocatalysis can reach full maturity at commercial level as an effective and economical process for treatment and purification of water and wastewater has recently intensified. Despite a bloom of scientific investigations in the last 30 years, particularly with regards to innovative photocatalytic materials, photocatalysis has so far seen a few industrial applications. Regardless of the points of view, it has been realized that research on reactor design and modeling are now equally urgent to match the extensive research carried out on innovative photocatalytic materials. In reality, the development of photocatalytic reactors has advanced steadily in terms of modeling and reactor design over the last two decades, though this topic has captured a smaller specialized audience. In this critical review, we introduce the latest developments on photocatalytic reactors for water treatment from an engineering perspective. The focus is on the modeling and design of photocatalytic reactors for water treatment at pilot- or at greater scale. Photocatalytic reactors utilizing both natural sunlight and UV irradiation sources are comprehensively discussed. The most promising photoreactor designs and models are examined giving key design guidelines. Other engineering considerations, such as operation, cost analysis, patents, and several industrial applications of photocatalytic reactors for water treatment are also presented. The dissemination of key photocatalytic reactor design principles among the scientific community and the water industry is currently one of the greatest obstacles in translating PWT research into widespread real-world application.

Present applications of titanium dioxide for the photocatalytic removal of pollutants from water: A review

The evolution of modern technology and industrial processes has been accompanied by an increase in the utilization of chemicals to derive new products. Water bodies are frequently contaminated by the presence of conventional pollutants such as dyes and heavy metals, as well as microorganisms that are responsible for various diseases. A sharp rise has also been observed in the presence of new compounds heretofore excluded from the design and evaluation of wastewater treatment processes, categorized as "emerging pollutants". While some are harmless, certain emerging pollutants possess the ability to cause debilitating effects on a wide spectrum of living organisms. Photocatalytic degradation has emerged as an increasingly popular solution to the problem of water pollution due to its effectiveness and versatility. The primary objective of this study is to thoroughly scrutinize recent applications of titanium dioxide and its modified forms as photocatalytic materials in the removal and control of several classes of water pollutants as reported in literature. Different structural modifications are used to enhance the performance of the photocatalyst such as doping and formation of composites. The principles of these modifications have been scrutinized and evaluated in this review in order to present their advantages and drawbacks. The mechanisms involved in the removal of different pollutants through photocatalysis performed by TiO2 have been highlighted. The factors affecting the mechanism of photocatalysis and those affecting the performance of different TiO2-based photocatalysts have also been thoroughly discussed, thereby presenting a comprehensive view of all aspects involved in the application of TiO₂ to remediate and control water pollution.

Aminated Polyethylene Terephthalate (PET) Nanofibers for the Selective Removal of Pb(II) from Polluted Water

Electrospun nanofibers have been successfully applied to remove toxic and carcinogenic contaminants such as heavy metals from polluted water. In this study, an efficient adsorbent based on poly(ethylene terephthalate) (PET) nanofibers was developed following a cheap, versatile and scalable process. PET nanofibers were first produced by electrospinning, and their surface was chemically functionalized using a simple aminolysis process. The capacity of the resulting material to adsorb Pb(II) from synthetic solutions was evaluated as a function of the contact time, pH, and initial metal ion concentration. The adsorbent system presented a quick kinetic adsorption, reaching an extremely high maximum adsorption capacity of about 50 millimol (mmol) of Pb(II) per gram of adsorbent system after just 30 min. Moreover, the effect of competing metal ions, such as Ni(II), Cd(II) and Cu(II), was studied at different molar ratios. Finally, when tested in continuous flow mode, aminated PET (APET) nanofibers were able to remove 97% of Pb(II) ions in solution, demonstrating their potential for the remediation of heavy metal-contaminated water.

Photoelectrochemical cell for simultaneous electricity generation and heavy metals recovery from wastewater

The feasibility of simultaneous recovery of heavy metals from wastewater (e.g., acid mining and electroplating) and production of electricity is demonstrated in a novel photoelectrochemical cell (PEC). The photoanode of the cell bears a nanoparticulate titania (TiO₂) film capped with the block copolymer [poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol)] hole scavenger, which consumed photogenerated holes, while the photogenerated electrons transferred to a copper cathode reducing dissolved metal ions and produced electricity. Dissolved silver Ag⁺, copper Cu²⁺, hexavalent chromium as dichromate Cr₂O₇^2- and lead Pb²⁺ ions in a mixture (0.2mM each) were removed at different rates, according to their reduction potentials. Reduced Ag⁺, Cu²⁺ and Pb²⁺ ions produced metal deposits on the cathode electrode which were mechanically recovered, while Cr₂O₇^2- reduced to the less toxic Cr³⁺ in solution. The cell produced a current density J_sc of 0.23mA/cm², an open circuit voltage V_oc of 0.63V and a maximum power density of 0.084mW/cm². A satisfactory performance of this PEC for the treatment of lead-acid battery wastewater was observed. The cathodic reduction of heavy metals was limited by the rate of electron-hole generation at the photoanode. The PEC performance decreased by 30% after 9 consecutive runs, caused by the photoanode progressive degradation.

Visible-light-driven photocatalytic inactivation of MS2 by metal-free g-C3N4: Virucidal performance and mechanism

The challenge to achieve effective water disinfection of pathogens, especially viruses, with minimized harmful disinfection byproducts calls for a cost-effective and environmentally benign technology. Here, polymeric graphitic carbon nitride (g-C₃N₄), as a metal-free robust photocatalyst, was explored for the first time for its ability to inactivate viruses under visible light irradiation. MS2 with an initial concentration of 1 × 10⁸ PFU/mL was completely inactivated by g-C₃N₄ with a loading of 150 mg/L under visible light irradiation of 360 min. g-C₃N₄ was a robust photocatalyst, and no decrease in its virucidal performance was observed over five cycles of sequential MS2 photocatalytic inactivation. The reactive oxygen species (ROSs) were measured by a range of scavengers, and photo-generated electrons and its derived ROSs (O- 2) were found to be the leading contributor for viral inactivation. TEM images indicated that the viral particle shape was distorted and the capsid shell was ruptured after photocatalysis. Viral surface proteins, particularly replicase proteins and maturation proteins, were damaged by photocatalytic oxidation. The loss of proteins would result in the leakage and rapid destruction of interior components (four main types of RNA genes), finally leading to viral death without regrowth. Our work opens a new avenue for the exploration and applications of a low-cost, high-efficient, and robust metal-free photocatalyst for green/sustainable viral disinfection.

The Promotion Effect and Mechanism of Methanoic Acid on the Photoelectrocatalytic Degradation of Fulvic Acid

A significant promotion effect of methanoic acid (MA) was proposed in the photoelectrocatalytic (PEC) degradation of fulvic acid (FA) and the degradation mechanism was also discussed. The PEC degradation property of FA and MA was investigated by an assembled thin-layer PEC reactor in which photoanode is TiO2nanotube arrays (TNAs) material. The result shows that only about 40% of FA was degraded, while MA could be completely degraded at the same condition. When mixing MA with FA, it shows a significant improvement in the degradation of FA. For instance, 50 mg/L FA mixed with 45 mg/L MA could achieve exhausted degradation. The results could be attributed to the promotion effect of MA that enhanced the generation of hydroxyl radicals, which maintain the continuous degradation of both FA and the intermediate products during the PEC process. This study proposed a new way of promoting the PEC degradation of FA as well as removing humus from the polluted water.

Efficient visible light photocatalytic degradation of 17α-ethinyl estradiol by a multifunctional Ag–AgCl/ZnFe2O4 magnetic nanocomposite

Magnetic separability and photocatalytic enhancement by plasmonic property of Ag–AgCl/ZnFe₂O₄ nanocomposite makes it practicable in both environmental and economic terms.

Visible-light-driven Ag/AgCl plasmonic photocatalysts via a surfactant-assisted protocol: enhanced catalytic performance by morphology evolution from near-spherical to 1D structures

Fibrous Ag/AgCl structures with boosted photocatalytic performances have been fabricatedviaa one-pot surfactant-assisted morphology evolution from near-spherical to 1D architectures.