Silver-modified mesoporous TiO2 photocatalyst for water purification

Efficient photocatalytic bactericidal performance of green-synthesised TiO2/reduced graphene oxide using banana peel extracts

In this study, the fabrication of titanium dioxide/reduced graphene oxide (TiO2/rGO) utilising banana peel extracts (Musa paradisiaca L.) as a reducing agent for the photoinactivation of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was explored. The GO synthesis was conducted using a modified Tour method, whereas the production of rGO involved banana peel extracts through a reflux method. The integration of TiO2 into rGO was achieved via a hydrothermal process. The successful synthesis of TiO2/rGO was verified through various analytical techniques, including X-ray diffraction (XRD), gas sorption analysis (GSA), Fourier-transform infrared (FT-IR) spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), scanning electron microscope-energy dispersive X-ray (SEM-EDX) and transmission electron microscopy (TEM) analyses. The results indicated that the hydrothermal-assisted green synthesis effectively produced TiO2/rGO with a particle size of 60.5 nm. Compared with pure TiO2, TiO2/rGO demonstrated a reduced crystallite size (88.505 nm) and an enhanced surface area (22.664 m2/g). Moreover, TiO2/rGO featured a low direct bandgap energy (3.052 eV), leading to elevated electrical conductivity and superior photoconductivity. To evaluate the biological efficacy of TiO2/rGO, photoinactivation experiments targeting E. coli and S. aureus were conducted using the disc method. Sunlight irradiation emerged as the most effective catalyst, achieving optimal inactivation results within 6 and 4 h.

Cu-doped mesoporous TiO2 photocatalyst for efficient degradation of organic dye via visible light photocatalysis

A solvothermal method was used to synthesize the mesoporous TiO2, (1-3w %) Cu-doped mesoporous TiO2 membrane with the help of a bioreactor. To understand the physicochemical composition of all synthesized nanomaterials, the structure, morphology and crystallinity of the materials were studied using X-ray diffractometer (XRD), Field emission scanning electron microscopy (FESEM), Fourier transform-infrared (FTIR), Energy dispersive X-ray spectroscopy (EDS) and cyclic voltammetry (CV). Under artificial light source (500 W mercury bulb) irradiations, the nano catalysts' catalytic effectiveness was examined for the azo dyes, namely Congo red. Cu-doping causes a shift in the light absorption of mTiO2 from the ultraviolet to the visible region. The 3w% Cu-doped mTiO2 photocatalyst exhibits lower band gap energy (2.6eV) than TiO2 which is 3.2 eV to efficiently utilize solar energy. As a result, the light absorption was shifted towards the visible spectrum. The recommended mTiO2 and (1, 2, 3) w% Cu-doped mTiO2 photocatalysts were used to photodegrade Congo red and methylene blue. For the degradation of CR, the mTiO2 photocatalyst exhibited 61% and 3w% Cu-doped mTiO2 demonstrated 99% photocatalytic performance after 50 min. A variety of scavengers were also utilized to distinguish the active species by catching the radicals and holes created during the process of photocatalytic degradation. CV indicates the presence of Cu2+ and Cu1+ in Cu-doped mTiO2. Oxygen vacancies and the electronegative surface of Cu1+ seem to perform the photocatalytic reduction of CR.

Sustainable application of nanoparticles in wastewater treatment: Fate, current trend & paradigm shift

Existing water and wastewater treatment techniques are becoming increasingly difficult to employ due to the discovery of new toxins, the rapid development of population and industrial activities, and the limited quantity of water resources. Treatment of wastewater is a critical need in modern civilization due to a scarcity of water resources and rising industrial activity. Some of the techniques utilized include adsorption, flocculation, filtration, and others, although they are only used for primary wastewater treatment. However, the development and deployment of modern wastewater management with high efficiency and low capitalization are critical in terms of mitigating the environmental consequences of waste. The employment of different nanomaterials in the treatment of wastewater has opened up a world of possibilities for heavy metal and pesticide removal, as well as the treatment of microbes and organic contaminants in wastewater. Nanotechnology is a rapidly evolving technology because of certain nanoparticle's outstanding physiochemical and biological capabilities as contrasted to bulk counterparts. Secondly, it has been established that this is a cost-effective treatment strategy with significant potential in wastewater management, transcending the limitations imposed by currently existing technology. Advances in nanotechnology to reduce water contamination have been presented in this review, including the use of various nanomaterials such as nanocatalysts, nanoadsorbents, and nanomembranes in the treatment of wastewater containing organic contaminants, hazardous metals, and virulent pathogens.

Rhodamine B dye degradation using used face masks-derived carbon coupled with peroxymonosulfate

Catalytic carbon materials from used face masks (UFM) activated by peroxymonosulfate (PMS) were developed for the degradation of rhodamine B (RhB) dye in aqueous solution. The UFM-derived carbon (UFMC) catalyst had a relatively large surface area as well as active functional groups and promoted the generation of singlet ¹O₂ and radicals from PMS, giving a high RhB degradation performance (98.1% after 3 h) in the presence of 3 mM PMS. The UFMC could degrade only 13.7% at a minimal RhB dose of 10^-5 M. The principal reactive oxygen species of sulphate (SO₄^•), hydroxyl radicals (^•OH), and singlet ¹O₂ were discovered using electron paramagnetic resonance and radical scavenger studies. Finally, a toxicological plant and bacterial study was performed to demonstrate the potential non-toxicity of the degraded RhB water sample.

Hierarchical 3D Flower-like Metal Oxides Micro/Nanostructures: Fabrication, Surface Modification, Their Crucial Role in Environmental Decontamination, Mechanistic Insights, and Future Perspectives

Hierarchical micro/nanostructures are constructed by micro-scaled objects with nanoarchitectures belonging to an interesting class of crystalline materials that has significant applications in diverse fields. Featured with a large surface-to-volume ratio, facile mass transportation, high stability against aggregation, structurally enhanced adsorption, and catalytical performances, three dimenisional (3D) hierarchical metal oxides have been considered as versatile functional materials for waste-water treatment. Due to the ineffectiveness of traditional water purification protocols for reclamation of water, lately, the use of hierarchical metal oxides has emerged as an appealing platform for the remediation of water pollution owing to their fascinating and tailorable physiochemical properties. The present review highlights various approaches to the tunable synthesis of hierarchical structures along with their surface modification strategies to enhance their efficiencies for the removal of different noxious substances. Besides, their applications for the eradication of organic and inorganic contaminants have been discussed comprehensively with their plausible mechanistic pathways. Finally, overlooked aspects in this field as well as the major roadblocks to the implementation of these metal oxide architectures for large-scale treatment of wastewater are provided here. Moreover, the potential ways to tackle these issues are also presented which may be useful for the transformation of current water treatment technologies.

Synthesis of mesoporous Ag/α-Fe2O3/TiO2 heterostructures with enhanced and accelerated photo/-catalytic reduction of 4-nitrophenol

4-Nitrophenol (4-NP) is reported to originate disadvantageous effects on the human body collected from industrial pollutants; therefore, the detoxification of 4-NP in aqueous contamination is strongly recommended. In this study, the heterojunction mesoporous α-Fe₂O₃/TiO₂ modulated with diverse Ag percentages has been constructed via a sol-gel route in the occurrence of a soft template P123. The formation of biphasic crystalline TiO₂ anatase and brookite phases has been successfully achieved with the average 10 nm particle sizes. The photo/-catalytic reduction of 4-NP has been performed utilizing NaBH₄ as a reducing agent with and without visible illumination. All Ag/Fe₂O₃/TiO₂ nanocomposites exhibited significantly higher photo/-catalytic reduction efficiency than pure Fe₂O₃, TiO₂ NPs, and Fe₂O₃/TiO₂ nanocomposite. 2.5% Ag/Fe₂O₃/TiO₂ nanocomposite was considered the highest and superior photocatalytic reduction efficiency, and it almost achieved 98% after 9 min. Interestingly, the photocatalytic reduction of 4-NP was accelerated 9 times higher than the catalytic reduction over 2.5% Ag/Fe₂O₃/TiO₂; its rate constant value was 709 and 706 times larger than pure TiO₂ and Fe₂O₃ NPs, respectively. The enhanced photocatalytic reduction ability of Ag/Fe₂O₃/TiO₂ nanocomposite might be referred to as significantly providing visible light absorption and a large surface area, and it can upgrade the effective separation and mobility of electron holes. The stability of the synthesized catalysts exhibited that the obtained catalysts can undergo a slight decrease in reduction efficiency after five successive cycles. This approach highlights a novel route for constructing ternary nanocomposite systems with high photo/-catalytic ability.

Facile Synthesis of Gram-Scale Mesoporous Ag/TiO2 Photocatalysts for Pharmaceutical Water Pollutant Removal and Green Hydrogen Generation

This work demonstrates a two-step gram-scale synthesis of presynthesized silver (Ag) nanoparticles impregnated with mesoporous TiO₂ and evaluates their feasibility for wastewater treatment and hydrogen gas generation under natural sunlight. Paracetamol was chosen as the model pharmaceutical pollutant for evaluating photocatalytic performance. A systematic material analysis (morphology, chemical environment, optical bandgap energy) of the Ag/TiO₂ photocatalyst powder was carried out, and the influence of material properties on the performance is discussed in detail. The experimental results showed that the decoration of anatase TiO₂ nanoparticles (size between 80 and 100 nm) with 5 nm Ag nanoparticles (1 wt %) induced visible-light absorption and enhanced charge carrier separation. As a result, 0.01 g/L Ag/TiO₂ effectively removed 99% of 0.01 g/L paracetamol in 120 min and exhibited 60% higher photocatalytic removal than pristine TiO₂. Alongside paracetamol degradation, Ag/TiO₂ led to the generation of 1729 μmol H₂ g^-1 h^-1. This proof-of-concept approach for tandem pollutant degradation and hydrogen generation was further evaluated with rare earth metal (lanthanum)- and nonmetal (nitrogen)-doped TiO₂, which also showed a positive response. Using a combination of ab initio calculations and our new theory model, we revealed that the enhanced photocatalytic performance of Ag/TiO₂ was due to the surface Fermi-level change of TiO₂ and lowered surface reaction energy barrier for water pollutant oxidation. This work opens new opportunities for exploiting tandem photocatalytic routes beyond water splitting and understanding the simultaneous reactions in metal-doped metal oxide photocatalyst systems under natural sunlight.

Hydrothermally-Derived Silver-Decorated Nanocrystalline Anatase Photocatalyst for Reactive Violet 2 Photodegradation

A photocatalyst comprised of Ag nanoparticles dispersed on an anatase matrix has been prepared using a simple hydrothermal method without additional thermal treatment. The prepared material was characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV-Vis spectroscopy, and N2 adsorption–desorption isotherms. The prepared catalyst activity was evaluated by photocatalytic degradation of C.I. Reactive Violet 2 (RV2) aqueous solution under UVA and visible light illumination. SEM revealed the non-uniform dispersion of silver particles throughout the matrix composed of fine particles. According to XRD analysis, the matrix was composed of pure anatase with a crystallite size of 8 nm calculated through the Scherrer equation. HRTEM micrograph analysis showed that anatase nanoparticles possess a spherical morphology and a narrow size distribution with an average particle size of 8 nm with more active anatase {100} crystal surface exposed, while silver nanoparticles were between 60 and 90 nm. A bandgap of 3.26 eV has been calculated on the basis of the DRS UV-Vis spectrum, while a specific surface area of 209 m2g−1 has been established from adsorption isotherms. Thus, through a simple synthesis approach without subsequent thermal treatment, the agglomeration of nanoparticles and the reduction of specific surface area have been avoided. Prepared nano Ag/anatase photocatalyst exhibits excellent efficiency for the photodegradation of RV2 under UVA and visible irradiation.

Bioactive Coatings Based on Nanostructured TiO2 Modified with Noble Metal Nanoparticles and Lysozyme for Ti Dental Implants

This work presents the synthesis of nanostructured TiO₂ modified with noble metal nanoparticles (Au, Ag) and lysozyme and coated on titanium foil. Moreover, the specific structural and functional properties of the resulting inorganic and hybrid materials were explored. The purpose of this study was to identify the key parameters for developing engineered coatings on titanium foil appropriate for efficient dental implants with intrinsic antibacterial activity. TiO₂ nanoparticles obtained using the sol-gel method were deposited on Ti foil and modified with Au/Ag nanoparticles. Morphological and structural investigations (scanning electron and atomic force microscopies, X-ray diffraction, photoluminescence, and UV-Vis spectroscopies) were carried out for the characterization of the resulting inorganic coatings. In order to modify their antibacterial activity, which is essential for safe dental implants, the following aspects were investigated: (a) singlet oxygen (¹O₂) generation by inorganic coatings exposed to visible light irradiation; (b) the antibacterial behavior emphasized by titania-based coatings deposited on titanium foil (TiO₂/Ti foil; Au-TiO₂/Ti foil, Ag-TiO₂/Ti foil); (c) the lysozyme bioactivity on the microbial substrate (Micrococcus lysodeicticus) after its adsorption on inorganic surfaces (Lys/TiO₂/Ti foil; Lys/Au-TiO₂/Ti foil, Lys/Ag-TiO₂/Ti foil); (d) the enzymatic activity of the above-mentioned hybrids materials for the hydrolysis reaction of a synthetic organic substrate usually used for monitoring the lysozyme biocatalytic activity, namely, 4-Methylumbelliferyl β-D-N,N',N″-triacetylchitotrioside [4-MU-β- (GlcNAc)₃]. This was evaluated by identifying the presence of a fluorescent reaction product, 7-hydroxy-4-metyl coumarin (4-methylumbelliferone).

Recent advances in nanoremediation: Carving sustainable solution to clean-up polluted agriculture soils

Agriculture is one of the foremost significant human activities, which symbolizes the key source for food, fuel and fibers. This activity results in a lot of ecological harms particularly with the excessive usage of chemical fertilizers and pesticides. Different agricultural practices have remained industrialized to advance food production, due to the growth in the world population and to meet the food demand through the routine use of more effective fertilizers and pesticides. Soil is intensely embellished by environmental contamination and it can be stated as "universal incline." Soil pollution usually occurs from sewage wastes, accidental discharges or as byproducts of chemical residues of unrestrained production of numerous materials. Soil pollution with hazardous materials alters the physical, chemical, and biological properties, causing undesirable changes in soil fertility and ecosystem. Engineered nanomaterials offer various solutions for remediation of contaminated soils. Engineered nanomaterial-enable technologies are able to prevent the uncontrolled release of harmful materials into the environment along with capabilities to combat soil and groundwater borne pollutants. Currently, nanobiotechnology signifies a hopeful attitude to advance agronomic production and remediate polluted soils. Studies have outlined the way of nanomaterial applications to restore the eminence of the environment and assist the detection of polluted sites, along with potential remedies. This review focuses on the latest developments in agricultural nanobiotechnology and the tools developed to combat soil or land and or terrestrial pollution, as well as the benefits of using these tools to increase soil fertility and reduce potential toxicity.

Preparation of molecularly imprinted Ag-TiO2 for photocatalytic removal of ethyl paraben

Herein, MI-Ag-TiO₂ was prepared by one-step sol-gel method, and its photocatalytic and characterization performance were fully analyzed. Within 120 min, the photocatalytic degradation rate of MI-Ag-TiO₂ to ethyl paraben was 93.4%, which was 1.48 times that of naked TiO₂. Compared with Ag-TiO₂, MI-TiO₂, and TiO₂, the photocatalytic selectivity of MI-Ag-TiO₂ to target pollutants increased by 24.5%, 31.5%, and 100%, respectively. Hence, the one-step molecular imprinting method can simply and quickly improve the photocatalytic performance of TiO₂. This research may help to further promote the practical application of molecularly imprinted photocatalysts in the future.

Photocatalytic disinfection of S. aureus using black TiO2−x under visible light

Reduced black TiO2−x was developed by a sol–gel combustion method. Evidence of reactive oxygen species production under visible light was obtained, and the material inactivated S. aureus by photocatalytic means under only visible light irradiation.

A Review on Metal Ions Modified TiO2 for Photocatalytic Degradation of Organic Pollutants

TiO2 is a semiconductor material with high chemical stability and low toxicity. It is widely used in the fields of catalysis, sensing, hydrogen production, optics and optoelectronics. However, TiO2 photocatalyst is sensitive to ultraviolet (UV) light; this is why its photocatalytic activity and quantum efficiency are reduced. To enhance the photocatalytic efficiency in the visible light range as well as to increase the number of the active sites on the crystal surface or inhibit the recombination rate of photogenerated electron–hole pairs electrons, various metal ions were used to modify TiO2. This review paper comprehensively summarizes the latest progress on the modification of TiO2 photocatalyst by a variety of metal ions. Lastly, the future prospects of the modification of TiO2 as a photocatalyst are proposed.

Critical review of photocatalytic disinfection of bacteria: from noble metals- and carbon nanomaterials-TiO2 composites to challenges of water characteristics and strategic solutions

This critical review covers ways to improve TiO₂-based photocatalysts, how water characteristics may affect photocatalytic disinfection, and strategies to tackle the challenges arising from water characteristics. Photocatalysis has shown much promise in the disinfection of water/wastewater, because photocatalysis does not produce toxic by-products, and is driven by green solar energy. There are however several drawbacks that are curbing the prevalence of photocatalytic disinfection applications: one, the efficiency of photocatalysts may limit popular utilization; two, the water characteristics may present some challenges to the process. TiO₂-based photocatalysts may be readily improved if composited with noble metals or carbon nanomaterials. Noble metals give TiO₂-based composites a higher affinity for dissolved oxygen, and induce plasmonic and Schottky effects in the TiO₂; carbon nanomaterials with a tunable structure, on the other hand, give the composites an improved charge carrier separation performance. Other than photocatalyst materials, the characteristics of water/wastewater is another crucial factor in the photocatalysis process. Also examined in this review are the crucial impacts that water characteristics have on photocatalysts and their interaction with bacteria. Accordingly, strategies to address the challenge of water characteristics on photocatalytic disinfection are explored: one, to modify the semiconductor conduction band to generate long-lifetime reactive species; two, to improve the interaction between bacteria and photocatalysts.

A novel ternary heterogeneous TiO2/BiVO4/NaY-Zeolite nanocomposite for photocatalytic degradation of microcystin-leucine arginine (MC-LR) under visible light

Microcystin-leucine arginine (MC-LR) is a carcinogenic toxin, produced by cyanobacteria. The release of this toxin into drinking water sources can threaten public health and environmental safety. Therefore, effective MC-LR removal from water resources is necessary. In the present study, the hydrothermal method was used to synthesize a novel ternary BiVO₄/TiO₂/NaY-Zeolite (B/T/N-Z) nanocomposite for MC-LR degradation under visible light. FESEM, FTIR, XRD, and DRS were performed for characterizing the nanocomposite structure. Also, the Response Surface Methodology (RSM) was applied to determine the impact of catalyst dosage, pH, and contact time on the MC-LR removal. High-performance liquid chromatography was performed to measure the MC-LR concentration. Based on the results, independent parameters, including contact time, catalyst dosage, and pH, significantly affected the MC-LR removal (P < 0.05). In other words, increasing the contact time, catalyst dosage, and acidic pH had positive effects on MC-LR removal. Among these variables, the catalyst dosage, with the mean square and F-value of 1041.37 and 162.84, respectively, had the greatest effect on the MC-LR removal efficiency. Apart from the interaction between the catalyst dosage and contact time, the interaction effects of other parameters were not significant. Also, the maximum MC-LR removal efficiency was 99.88% under optimal conditions (contact time = 120 min, catalyst dosage = 1 g/L, and pH = 5). According to the results, the B/T/N-Z nanocomposite, as a novel and effective photocatalyst could be used to degrade MC-LR from polluted water.

Effect of Hybrid mono/bimetallic Nanocomposites for an enhancement of Catalytic and Antimicrobial Activities

Exploring the new catalytic systems for the reduction of organic and inorganic pollutants from an indispensable process in chemical, petrochemical, pharmaceutical and food industries, etc. Hence, in the present work, authors motivated to synthesize bare reduced graphene oxide (rGO), polyaniline (PANI), three different ratios of rGO-PANI_{(80:20,50:50, 10:90)} composites and rGO-PANI_{(80:20,50:50, 10:90)} supported mono (Pd) & bimetallic [Pd: Au_{(1:1,1:2, 2:1)}] nanocomposite by a facile chemical reduction method. Also, it investigated their catalytic performances for the reduction of organic/inorganic pollutants and antimicrobial activities. All the freshly prepared bare rGO, PANI, three different ratios of rGO-PANI_{(80:20, 50:50,10:90)} composites and rGO-PANI_{(80:20, 50:50,10:90)}/Pd & Pd: Au_{(1:1, 1:2,2:1)} nanocomposite hybrid catalysts were characterized using UV-Vis, FT-IR, SEM, FE-SEM, EDAX, HR-TEM, XRD, XPS and Raman spectroscopy analysis. Among them, an optimized best composition of rGO-PANI_(80:20)/Pd: Au_(1:1) bimetallic nanocomposite hybrid catalyst exhibits better catalytic reduction and antimicrobial activities than other composites, as a result of strong electrostatic interactions between rGO, PANI and bimetal (Pd: Au) NPs through a synergistic effect. Hence, an optimized rGO-PANI_(80:20)/Pd:Au_(1:1) bimetallic nanocomposite catalyst would be considered as a suitable catalyst for the reduction of different nitroarenes, organic dyes, heavy metal ions and also significantly inhibit the growth of S. aureus, S. Typhi as well as Candida albicans and Candida kruesi in wastewater.

Fabrication of metal-free PTET-T-COOH/g-C3N4 heterostructure for enhancing photocatalytic activity

In this research work, we successfully fabricated a range of PTET-T-COOH/g-C₃N₄ heterostructures via a simple method. The as-prepared PTET-T-COOH/g-C₃N₄ heterostructures show enhanced photocatalytic degradation activity as compared to pure g-C₃N₄. For the photocatalytic degradation of RhB, the optimal PTET-T-COOH/g-C₃N₄-1% heterostructure is nearly 3.83 times that of the pure g-C₃N₄. The enhancement of photocatalytic performance is ascribed to three aspects: one is the strong interaction between PTET-T-COOH and g-C₃N₄; the second is the larger surface area of the PTET-T-COOH/g-C₃N₄ heterostructure compared to that of pure g-C₃N₄; the third is the effectively improved transferability of photogenerated carriers. In addition, the whole photocatalytic reaction mechanism over the PTET-T-COOH/g-C₃N₄ heterostructure is provided. This work may offer a hopeful method to synthesize any other heterostructure with high stability and superior photocatalytic activity.

The metal-free PTET-T-COOH/g-C₃N₄ heterostructure exhibits a high degradation rate for RhB under visible light irradiation.

A highly efficient nano-graphite-doped TiO2 photocatalyst with a unique sea-island structure for visible-light degradation

A nano-graphite-doped TiO₂ composite, C-TiO₂, was fabricated by atomic layer deposition (ALD) of TiO₂ onto carbon fiber fabrics (CFFs), followed by calcination.

Iodine ion doped bromo bismuth oxide modified bismuth germanate: A direct Z-scheme photocatalyst with enhanced visible-light photocatalytic performance

A series of Z-scheme I-BiOBr/Bi₁₂GeO₂₀ heterostructures were successfully obtained by a simple method. The Z-scheme I-BiOBr/Bi₁₂GeO₂₀ heterostructures show outstanding photocatalytic performance for degrading the various organic pollutants of the waste water. For degradation of Tetracycline (TC), the Z-scheme 30I-BiOBr/Bi₁₂GeO₂₀ heterostructure exhibits the superior rate constant, which is about 7.73 times, 3.52 times and 1.66 times higher than that of the pure Bi₁₂GeO₂₀, BiOBr and I-BiOBr, respectively. Meanwhile, as we expected, the Z-scheme 30I-BiOBr/Bi₁₂GeO₂₀ heterostructure also displays the enhanced photocatalytic perfomance for degradation of Ciprofloxacin (CIP), 2-Mercaptobenzothiazole (MBT) and reduction of aqueous Cr(VI). The enhancement of photocatalytic performance is attributed to the high redox capacity and the strong interfacial interaction between I-BiOBr and Bi₁₂GeO₂₀, which can effectively improve the separation of photo-induced electron-hole pairs. Additionally, the photocatalytic mechanism over the Z-scheme I-BiOBr/Bi₁₂GeO₂₀ heterostructure is provided. The research work may provide a promising approach to fabricate other Z-scheme heterostructures with efficient photocatalytic performance.

Titanium dioxide modified with silver by two methods for bactericidal applications

“Titanium dioxide (TiO₂) is a semiconductor material that exhibits antibacterial activity due to its photocatalytic properties under ultraviolet light. On the other hand, silver also exhibits strong antibacterial activity towards a wide range of microorganisms and TiO₂ with silver addition exhibits more efficient photocatalytic properties than unmodified TiO₂. In this work, TiO₂ nanoparticles were synthesized by the hydrothermal method and modified with silver by two different methods: wet impregnation (Ex situ) and In situ incorporation. The antimicrobial activity of TiO₂ nanoparticles synthesized and modified by both methods was evaluated against Escherichia coli and Staphylococcus aureus. The results showed that TiO₂ nanoparticles have anatase phase. Also, spherical morphology with a mean particle size around 10.6 nm was obtained. The presence of silver in the modified TiO₂ nanoparticles was confirmed by EDS and XPS. TiO₂ particles modified by the Ex situ method, showed a better bactericidal activity compared to the particles modified by In situ incorporation method and TiO₂ unmodified nanoparticles. This study demonstrated that both methods used to modify the titanium dioxide nanoparticles are effective as bactericidal materials and better results were found for the Ex situ method.”

A facile phase transformation strategy for fabrication of novel Z-scheme ternary heterojunctions with efficient photocatalytic properties

With increasing pollution of water resources and demand for hydrogen energy, photocatalysis, as a "green chemistry" technology, has attracted great attention. To meet the practical application requirements, photocatalysts should possess enhanced efficiency and be of low cost. Here, a novel Z-scheme ternary ZnTiO3/Zn2Ti3O8/ZnO heterojunction has been prepared by a solvothermal-calcination process. The phase transformation process of the sample can be defined as two processes, dehydration and thermal decomposition (ZnTiO3 → Zn2Ti3O8 + ZnO). The ZnTiO3/Zn2Ti3O8/ZnO heterojunction produced in this facile phase transformation strategy displayed highly efficient photocatalytic performance in water splitting for hydrogen production and pollutant removal, e.g. phenol, dye, and heavy metal Cr(vi). On the basis of the PL spectra, photocurrent response, radical trapping experiments and ESR tests, we found that a nontraditional transport of photoinduced carriers created by a single Z-scheme mechanism played a significant role in the efficient removing of target pollutants and hydrogen generation. This work provides a facile phase transformation approach to construct a Z-scheme semiconductor heterostructure system with high efficiency for hydrogen production and water pollution treatment.

Synergistic effects of multi-active sites in silver modified Bi°-BiVO4 toward efficient reduction of aromatic nitrobenzene

In this work, we report on the preparation of silver nanoparticles modified bismuth/bismuth vanadate (Bi°-BiVO₄) catalyst with multi-active sites toward efficient reduction of aromatic nitrobenzene, aiming to tailor the synergistic effects of multi-active sites and specify the underlying catalytic mechanism. The as-prepared catalysts were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray and X-ray photoelectron spectroscopy. It is observed that Ag nanoparticles with diameter of ˜30 nm were anchored evenly on the surface of rod-shaped BiVO₄, which offered multi-active sites to contact with the reactants effectively and transfer interfacial electron to 4-nitrophenol (4-NP) rapidly. The activity factor k of Ag/Bi°-BiVO₄ for 4-NP reduction is estimated to ˜3933.4 min^-1 g^-1, which is much higher than that obtained from pristine BiVO₄ catalyst, Bi° and noble metal Ag nanoparticles. According to the experimental results, the reaction mechanism and reaction path of 4-NP reduction for BiVO₄, Bi and Ag were studied through the density functional theory (DFT) theoretical calculation, which suggested that they exhibit synergistic catalytic effect in the reaction process. This work may provide a feasible foundation for the mechanism research of semiconductor reduction to 4-nitrophenol.

Structures, mechanical properties and antibacterial activity of Ag/TiO2 nanocomposite materials synthesized via HVPG technique for coating application

In this study, the structures and mechanical properties of the silver-titanium dioxide nanocomposite material were investigated using Atomic Force Microscopy (AFM). These properties include surface roughness, hardness, and reduced Young's modulus. The nanocomposite material was successfully synthesized using the Horizontal Vapor Phase Growth (HVPG) technique which yielded shapes such as nanoparticles, nanospheres, nanorods, triangular nanocomposites, and nanocrystals. Characterization of nanocomposite materials was done through Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) spectroscopy to elucidate material shape, diameter, and composition. The pour plate technique combined with McFarland standards was used to evaluate the antibacterial activity of the nanocomposite material against Staphylococcus aureus. The nanocomposite material was able to eradicate bacteria and was suitable for coating applications effectively.

The Technology Horizon for Photocatalytic Water Treatment: Sunrise or Sunset?

Advanced oxidation processes via semiconductor photocatalysis for water treatment have been the subject of extensive research over the past three decades, producing many scientific reports focused on elucidating mechanisms and enhancing kinetics for the treatment of contaminants in water. Many of these reports imply that the ultimate goal of the research is to apply photocatalysis in municipal water treatment operations. However, this ignores immense technology transfer problems, perpetuating a widening gap between academic advocation and industrial application. In this Feature, we undertake a critical examination of the trajectory of photocatalytic water treatment research, assessing the viability of proposed applications and identifying those with the most promising future. Several strategies are proposed for scientists and engineers who aim to support research efforts to bring industrially relevant photocatalytic water treatment processes to fruition. Although the reassessed potential may not live up to initial academic hype, an unfavorable assessment in some areas does not preclude the transfer of photocatalysis for water treatment to other niche applications as the technology retains substantive and unique benefits.

A comprehensive review on the use of second generation TiO2 photocatalysts: Microorganism inactivation

Photocatalytic disinfection practices have been applied for decades and attract current interest along with the developments in synthesis of novel photocatalysts. A survey based investigation was performed for elucidation of photocatalytic treatment details as well as disinfection mechanism of microorganisms. The present work brings significant information on the utilization of second generation TiO₂ photocatalysts for inactivation of microorganisms typically using E. coli as the model microorganism. Special interest was devoted to the role of organic matrix either generated during treatment or as a natural component. Studies on photocatalytic disinfection were extensively reviewed and evaluated with respect to basic operational parameters related to photocatalysis, and types and properties of microorganisms investigated. Degradation mechanism and behavior of microorganisms towards reactive oxygen species during disinfection and organic matrix effects were also addressed. For successful utilization and effective assessment of visible light active photocatalysts, standard protocols for disinfection activity testing have to be set. Further improvement of the efficiency of these materials would be promising for future applications in water treatment processes.

Nanotechnology for Environmental Remediation: Materials and Applications

Environmental remediation relies mainly on using various technologies (e.g., adsorption, absorption, chemical reactions, photocatalysis, and filtration) for the removal of contaminants from different environmental media (e.g., soil, water, and air). The enhanced properties and effectiveness of nanotechnology-based materials makes them particularly suitable for such processes given that they have a high surface area-to-volume ratio, which often results in higher reactivity. This review provides an overview of three main categories of nanomaterials (inorganic, carbon-based, and polymeric-based materials) used for environmental remediation. The use of these nanomaterials for the remediation of different environmental contaminants-such as heavy metals, dyes, chlorinated organic compounds, organophosphorus compounds, volatile organic compounds, and halogenated herbicides-is reviewed. Various recent examples are extensively highlighted focusing on the materials and their applications.

Hierarchically-structured SiO2-Ag@TiO2 hollow spheres with excellent photocatalytic activity and recyclability

A new protocol for constructing sandwich-like SiO₂-Ag@TiO₂ hollow spheres (SAT) is introduced, in which SiO₂ acts as an efficient support for the Ag nanoparticles (Ag NPs) immobilization, while TiO₂ maintains its hierarchical structure and prevents the aggregation of Ag NPs during the photocatalytic reaction. As a photocatalytic agent, the inner and outer surfaces of TiO₂ can be fully occupied by pollutants molecules because of its unique structure, which faster boosts the photo-generated electrons to transfer the substrates, leading to an enhanced photocatalytic performance. Compared with Ag NPs deposited on the surface of SiO₂@TiO₂ (STA), the as-synthesized SAT exhibits a markedly enhanced visible-light and UV light activity than STA for degrading tetracycline and traditional dyes. The excellent photocatalytic performances are ascribed to the enhanced transport paths of photo-generated electrons, reduced recombination probability of e^-/h⁺ pairs, and decreased threat of oxidation and corrosion. Especially, the SAT still maintains its photocatalytic efficiency after five consecutive runs even though the sample is recovered under visible-light irradiation, far beyond the reusability of STA under the same conditions. Therefore, the outstanding photocatalytic activity and excellent recyclability make SAT more potential to purify aquatic contaminants and to meet the demands of future environmental issues.

Facile synthesis of dispersed Ag nanoparticles on chitosan-TiO2 composites as recyclable nanocatalysts for 4-nitrophenol reduction

This paper presents a facile, rapid, and controllable procedure for the recovery of trace Ag⁺ ions and in situ assembly of well dispersed Ag nanoparticles on chitosan-TiO₂ composites through bioaffinity adsorption followed by photocatalytic reduction. The prepared Ag nanoparticles are proven to be efficient and recyclable nanocatalysts for the reduction of 4-nitrophenol to 4-aminophenol in the presence of NaBH₄. Well dispersed quasi-spherical Ag NPs are synthesized in 20 min in the designed inner-irradiated photocatalytic system under a wide range of Ag⁺ concentrations (50-200 mg l^-1), temperatures (10 °C-25 °C) conditions, and UV or visible light irradiation. The synthesized Ag NPs can catalyze the reduction of 4-nitrophenol by NaBH₄ at 100% conversion in 120 min and preserve the catalytic activity in five successive cycles. This procedure for trace Ag⁺ ions recovery and Ag NPs assembly has the potential to be scaled up for the mass production of recyclable Ag nanocatalysts. The present work provides a green and efficient procedure for the conversion of hazardous 4-nitrophenol to industrially important 4-aminophenol and also sheds a light on designing scaled-up procedures for treating high volumes of wastewater with dilute heavy metals to produce recyclable metallic nanocatalysts in aqueous systems.

TiO2 nanotubes/Ti plates modified by silver–benzene with enhanced photocatalytic antibacterial properties

A novel Ag/Benzene-Mod/TiO₂ nanotubes/Ti plate was fabricated via photo-modification by benzene, followed by electrodeposition of Ag on the TiO₂ nanotubes/Ti plate.

A highly selective conversion of toxic nitrobenzene to nontoxic aminobenzene by Cu2O/Bi/Bi2MoO6

Cu₂O/Bi/Bi₂MoO₆, a ternary catalyst, was expertly prepared using an in situ catalytic reduction reaction.

Performance and Mechanism of Piezo-Catalytic Degradation of 4-Chlorophenol: Finding of Effective Piezo-Dechlorination

Piezo-catalysis was first used to degrade a nondye pollutant, 4-chlorophenol (4-CP). In this process, hydrothermally synthesized tetragonal BaTiO₃ nano/micrometer-sized particles were used as the piezo-catalyst, and the ultrasonic irradiation with low frequency was selected as the vibration energy to cause the deformation of tetragonal BaTiO₃. It was found that the piezoelectric potential from the deformation could not only successfully degrade 4-chlorophenol but also effectively dechlorinate it at the same time, and five kinds of dechlorinated intermediates, hydroquinone, benzoquinone, phenol, cyclohexanone, and cyclohexanol, were determined. This is the first sample of piezo-dechlorination. Although various active species, including h⁺, e^-, •H, •OH, •O₂^-, ¹O₂, and H₂O₂, were generated in the piezoelectric process, it was confirmed by ESR, scavenger studies, and LC-MS that the degradation and dechlorination were mainly attributed to •OH radicals. These •OH radicals were chiefly derived from the electron reduction of O₂, partly from the hole oxidation of H₂O. These results indicated that the piezo-catalysis was an emerging and effective advanced oxidation technology for degradation and dechlorination of organic pollutants.

Bactericidal mechanisms and effector targets of TiO2 and &nbsp;Ag-TiO2 against Staphylococcus aureus

Purpose

In our previous study, Ag⁺-loaded TiO₂ and Ag⁺-loaded SiO₂ coatings for tracheal intubation were prepared to prevent ventilator-associated pneumonia (VAP), but the antimicrobial targets and the underlying mechanisms of TiO₂ and Ag-TiO₂ (Ag⁺) are still unclear. We attempted to elucidate the antimicrobial activity and potential mechanisms against Staphylococcus aureus.

Methodology

The study tested the TiO₂ and Ag⁺ bacteriostatic activity against S. aureus strains by MIC assays and S. aureus growth curves, lesion in the membranes by surface hydrophobicity tests, conductivity tests and measurements of DNA and RNA contents in S. aureus cultures, and investigated the inhibition of soluble protein and nucleic acid synthesis by measurements of soluble protein content, fluorescent intensity and nucleic acid content of living S. aureus.

Results

The MIC values of TiO₂ and Ag⁺ were 1.6 mg ml⁻¹ and 5.781 µg ml⁻¹. TiO₂ and Ag⁺ could inhibit the growth of S. aureus. After treatment with TiO₂ and Ag⁺, the surface hydrophobicity was significantly reduced, the conductivity of cultures increased, and DNA and RNA content in cultures showed no obvious changes. The expressions of soluble proteins and nucleic acid contents of living S. aureus were reduced after treatment with TiO₂ and Ag⁺.

Conclusion

TiO₂ and Ag⁺ could cause slight lesion in the membrane to affect S. aureus membrane permeability, but not decomposition of membrane. Moreover, TiO₂ and Ag⁺ could lead to reduced expression of soluble protein by inhibiting the synthesis of nucleic acids, thereby further inhibiting the growth of S. aureus.

Photoelectrocatalytic inactivation of fecal coliform bacteria in urban wastewater using nanoparticulated films of TiO2 and TiO2/Ag

Photocatalysis has shown the ability to inactivate a wide range of harmful microorganisms with traditional use of chlorination. Photocatalysis combined with applied bias potential (photoelectrocatalysis) increases the efficiency of photocatalysis and decreases the charge recombination. This work examines the inactivation of fecal coliform bacteria present in real urban wastewater by photoelectrocatalysis using nanoparticulated films of TiO₂ and TiO₂/Ag (4%w/w) under UV light irradiation. The catalysts were prepared with different thicknesses by the sol-gel method and calcined at 400°C and 600°C. The urban wastewater samples were collected from the sedimentation tank effluent of the university sewage treatment facility. The rate of bacteria inactivation increases with increasing the applied potential and film thicknesses; also, the presence of silver on the catalyst surface annealed at 400°C shows better inactivation than that at 600°C. Finally, a structural cell damage of Escherichia coli (DH5α), inoculated in water, is observed during the photoelectrocatalytic process.