TiO2 photocatalysis: Design and applications

Photocatalytic destruction of volatile aromatic compounds by platinized titanium dioxide in relation to the relative effect of the number of methyl groups on the benzene ring

The photocatalytic destruction (PCD) of volatile organic compounds (VOC) into environmentally benign compounds is one of the most ideal routes for the management of indoor air quality. It is nevertheless not easy to achieve the mineralization of aromatic VOC through PCD technology because of their recalcitrant structures (i.e., conjugated π benzene ring). In this research, the PCD potential against three model aromatic hydrocarbons (i.e., benzene (B), toluene (T), and m-xylene (X): namely, BTX) has been explored using a titanium dioxide (TiO₂) supported platinum (Pt) catalyst after the high-temperature hydrogen (H₂)-based reduction (R) pre-treatment (i.e., Pt/TiO₂-R). The effects of the key process variables (e.g., relative humidity (RH), oxygen (O₂) content, flow rate, VOC concentration, and the co-presence of VOC) on the PCD efficiency and related mechanisms were also assessed in detail. The PCD efficiency is seen to increase with the rise in the increasing number of methyl groups on the benzene ring (in the order of benzene (46.5%), toluene (68.2%), and m-xylene (95.9%)), as the adsorption and activation of the VOC molecule on the photocatalyst surface are promoted by the increased distribution of electrons on the benzene ring. The BTX were oxidated subsequently by the photogenerated reactive oxygen species (ROS), i.e., the hydroxyl radicals (•OH) and superoxide anion radicals (•O₂^-). The overall results of this study are expected to help expand the applicability of photocatalysis towards air quality management by offering detailed insights into the factors and processes governing the photocatalytic decomposition of aromatic VOCs.

Improvement of the Photocatalytic Activity of Au/TiO2 Nanocomposites by Prior Treatment of TiO2 with Microplasma in an NH3 and H2O2 Solution

Plasmonic photocatalytic nanocomposites of TiO2 and Au nanoparticles (NPs) have recently attracted the attention of researchers, who aim to improve the photocatalytic activity of potential TiO2 NPs. In this study, we report photocatalytic activity enhancement for a Au/TiO2 nanocomposite prepared by the plasma–liquid interaction method using an atmospheric microplasma apparatus. The enhanced photocatalytic activity of the prepared Au/TiO2 is demonstrated by the degradation of methylene blue (MB) in water under both ultraviolet (UV) and visible light irradiation. The prior treatment of TiO2 with microplasma in a NH3 and H2O2 solution is found to strongly improve the photocatalytic activity of both the treated TiO2 NPs, as well as the synthesized Au/TiO2 nanocomposite.

α- and β-Ag4P2S7: Two Semiconductors with Promising Photocatalytic Hydrogen Production Based on a Density Functional Theory Study

Herein, a new chiral compound with short Ag-Ag distances, namely, β-Ag₄P₂S₇ (P3₁21), has been discovered by a solid-state method. Density functional theory (DFT) calculations show that both α and β phases exhibit suitable band gaps, low reduction potentials, and large visible-light absorption coefficients, as well as excellent band edges for carrier separation, suggesting their promising application in photocatalytic hydrogen production.

Preparation and Photocatalytic Performance of TiO2 Nanowire-Based Self-Supported Hybrid Membranes

Nowadays, the use of hybrid structures and multi-component materials is gaining ground in the fields of environmental protection, water treatment and removal of organic pollutants. This study describes promising, cheap and photoactive self-supported hybrid membranes as a possible solution for wastewater treatment applications. In the course of this research work, the photocatalytic performance of titania nanowire (TiO₂ NW)-based hybrid membranes in the adsorption and degradation of methylene blue (MB) under UV irradiation was investigated. Characterization techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray powder diffractometry (XRD) were used to study the morphology and surface of the as-prepared hybrid membranes. We tested the photocatalytic efficiency of the as-prepared membranes in decomposing methylene blue (MB) under UV light irradiation. The hybrid membranes achieved the removal of MB with a degradation efficiency of 90% in 60 min. The high efficiency can be attributed to the presence of binary components in the membrane that enhanced both the adsorption capability and the photocatalytic ability of the membranes. The results obtained suggest that multicomponent hybrid membranes could be promising candidates for future photocatalysis-based water treatment technologies that also take into account the principles of circular economy.

pH dependent synthesis and characterization of bismuth molybdate nanostructure for photocatalysis degradation of organic pollutants

Bismuth molybdate (Bi₂MoO₆) nanostructures has attracted many researches as an advanced photocalysts for the organic contaminants. In this paper, bismuth molybdate Bi₂MoO₆ nanoparticles were synthesized using a simple hydrothermal method at varied pH (2, 4, 6, 8, and 10) for 15 h at 180 °C. The results reveal the variation pH precursor solutions have a significant impact on the morphology, phase formations, and photocatalytic activity of samples. The synthesized samples at low pH level were characterized by FESEM analysis revealing Bi₂MoO₆ nanoplates have formed while gradually convert to Bi₂MoO₆ spherical nanoparticle at high PH level as shown in energy dispersive X-ray spectroscopy (DES) peaks. The X-ray diffraction patterns reveal characteristic peaks corresponding to mixed phases of Bi₂MoO₆ and cubic Bi₄MoO₉ at high pH value. The optical absorption study exhibit Bi₂MoO₆ nanoplates absorbed visible light with blue shift when compared to the cubic Bi₄MoO₉ structures. Moreover, the photocatalytic activity results revealed that nanoplates in pH = 4 sample has excellent photocatalytic activity for degradation of rhodamine (RhB), methylene orange (MO), and phenol under visible-light irradiation (λ > 400 nm) as well as exhibit the photodegradation 90% of phenol within 300 min.

Mechano-Nanoarchitectonics: Design and Function

Mechanical stimuli have rather ambiguous and less-specific features among various physical stimuli, but most materials exhibit a certain level of responses upon mechanical inputs. Unexplored sciences remain in mechanical responding systems as one of the frontiers of materials science. Nanoarchitectonics approaches for mechanically responding materials are discussed as mechano-nanoarchitectonics in this review article. Recent approaches on molecular and materials systems with mechanical response capabilities are first exemplified with two viewpoints: i) mechanical control of supramolecular assemblies and materials and ii) mechanical control and evaluation of atom/molecular level structures. In the following sections, special attentions on interfacial environments for mechano-nanoarchitectonics are emphasized. The section entitled iii) Mechanical Control of Molecular System at Dynamic Interface describes coupling of macroscopic mechanical forces and molecular-level phenomena. Delicate mechanical forces can be applied to functional molecules embedded at the air-water interface where operation of molecular machines and tuning of molecular receptors upon macroscopic mechanical actions are discussed. Finally, the important role of the interfacial media are further extended to the control of living cells as described in the section entitled iv) Mechanical Control of Biosystems. Pioneering approaches on cell fate regulations at liquid-liquid interfaces are discussed in addition to well-known mechanobiology.

Cu Modified TiO2 Catalyst for Electrochemical Reduction of Carbon Dioxide to Methane

Electrochemical reduction of CO2 (ECO2R) is gaining attention as a promising approach to store excess or intermittent electricity generated from renewable energies in the form of valuable chemicals such as CO, HCOOH, CH4, and so on. Selective ECO2R to CH4 is a challenging target because the rate-determining step of CH4 formation, namely CO* protonation, competes with hydrogen evolution reaction and the C–C coupling toward the production of longer-chain chemicals. Herein, a Cu-TiO2 composite catalyst consisting of CuOx clusters or Cu nanoparticles (CuNPs), which are isolated on the TiO2 grain surface, was synthesized using a one-pot solvothermal method and subsequent thermal treatment. The Cu-TiO2 catalyst exhibited high selectivity for CH4, and the ratio of FE for CH4 to total FE for all products in ECO2R reached 70%.

Fabrication and Characterization of Inverse-Opal Titania Films for Enhancement of Photocatalytic Activity

Novel materials with a periodic structure have recently been intensively studied for various photonic and photocatalytic applications due to an efficient light harvesting ability. Here, inverse opal titania (IOT) has been investigated for possible enhancement of photocatalytic activity. The IOT films were prepared on a glass support from silica and polystyrene (PS) opals by sandwich-vacuum-assisted infiltration and co-assembly methods, respectively. The reference sample was prepared by the same method (the latter) but with PS particles of different sizes, and thus without photonic feature. The modification of preparation conditions was performed to prepare the films with a high quality and different photonic properties, i.e., photonic bandgap (PBG) and slow photons’ wavelengths. The morphology and optical properties were characterized by scanning electron microscopy (SEM) and UV/vis spectroscopy, respectively. The photocatalytic activity was evaluated (also in dependence on the irradiation angle) for oxidative decomposition of acetaldehyde gas under irradiation with blue LED by measuring the rate of evolved carbon dioxide (CO2). It has been found that PBG wavelength depends on the size of particles forming opal, the void diameter of IOT, and irradiation angle, as expected from Bragg’s law. The highest activity (more than two-fold enhancement in the comparison to the reference) has been achieved for the IOT sample of 226-nm void diameter and PBG wavelengths at 403 nm, prepared from almost monodisperse PS particles of 252-nm diameter. Interestingly, significant decrease in activity (five times lower than reference) has been obtained for the IOT sample of also high quality but with 195-nm voids, and thus PBG at 375 nm (prohibited light). Accordingly, it has been proposed that the perfect tunning of photonic properties (here the blue-edge slow-photon effect) with bandgap energy of photocatalyst (e.g., absorption of anatase) results in the improved photocatalytic performance.

Use of porphyrin-containing polymers of intrinsic microporosity as selective photocatalysts for oxidative detoxification of chemical warfare agent simulant

Porphyrin-based polymers of intrinsic microporosity (PIMs) in photocatalytic degradation of a mustard-gas simulant (2-chloroethyl ethyl sulfide (2-CEES)) was demonstrated. Under blue-ultraviolet (UV) light-emitting diode (LED) irradiation, porphyrin-based PIMs PP-H2 and PP-Zn(II) worked as effective heterogeneous photocatalysts for oxidation of 2-CEES. Solvent played an important role in the conversion and selectivity of 2-CEES oxidation. When AcCN was used as a solvent, PP-H2and PP-Zn(II) demonstrated complete conversion of 2-CEES in 30 and 50 min, respectively, whereas they showed complete conversion at 60 and 70 min, respectively, when MeOH was used as a solvent. Moreover, these PIMs produced 2-chloroethyl ethyl sulfoxide (2-CEESO) as a major product with small amounts of 2-chloroethyl ethyl sulfone (2-CEESO[Formula: see text], ethyl methoxyethyl sulfoxide (EMSO), and vinyl sulfoxide (EVS) as side products in most solvents. However, when MeOH was used as a solvent, highly toxic 2-CEESO2 was not observed as a side product. Furthermore, these PIMs showed no significant changes in photocatalytic activity even after five cycles of reuse, indicating their high stability. Thus, the series of PIMs prepared herein can perform well as heterogeneous catalysts in photooxidation of 2-CEES under blue-UV LED light, with PP-H2 being the most effective oxidation catalyst, leading to fast conversion and high selectivity.

Photocatalytic Activity in the In-Flow Degradation of NO on Porous TiO2–Coated Glasses from Hybrid Inorganic–Organic Thin Films Prepared by a Combined ALD/MLD Deposition Strategy

A combined ALD/MLD (where ALD and MLD stand for atomic and molecular layer deposition, respectively) deposition strategy using TiCl4, H2O and HQ (hydroquinone) as precursors has been applied for the preparation of inorganic–organic thin films on soda-lime glasses. The alternate deposition of TiO2 layers, by pulsing TiCl4/H2O (ALD), and hybrid layers, using TiCl4/HQ (MLD), results in the formation of thin films that are precursors for porous TiO2-coatings after removal of the HQ template by annealing. The coated-glassed show good photocatalytic activity in the degradation of NO with up to 15% reduction of NO concentration in three successive photocatalytic cycles of 5 h each. Surface Scanning Electron Microscopy (SEM) images show that the TiO2-coating is composed of large grains that are made up of finer subgrains resulting in a porous structure with an average pore size of 3–4 nm. Transmission Electron Microscopy (TEM) images show two regions, a porous columnar structure on top and a denser region over the glass substrate. Energy Dispersive X-Ray (EDX) analysis, nanocrystal electron diffraction and Raman spectroscopy confirm the presence of the anatase phase, which, together with the porosity of the material, accounts for the observed photocatalytic activity.

Controlling microbial activity on walls by a photocatalytic nanocomposite paint: A field study

BACKGROUND

Bacteria and fungi that grow on the walls can cause allergic reactions and infectious diseases in human. We proposed a low-cost and easy-to-operate testing protocol for large scale field studies to evaluate the long-term antimicrobial performance of a novel WO_x paint in 2 primary schools.

METHODS

In Tun Mun and Tin Shui Wai schools, WO_x paints were painted on semi-outdoor and indoor walls and daily chlorine disinfection was applied after class in TSW School. A guidance was proposed for the protocol using the ATP biofluorescence method for large-scale field studies. ATP swab samples were taken at locations with and without the WO_x paint on a control basis with a sampling frequency once a week for three months. The ATP values were then processed and presented in box plots.

RESULTS

In both schools, the median log-scale ATP values of walls with WOx paint were at least 0.5-log lower than those without WOx paint. The WO_x paint also performed better than daily chlorine disinfection in reducing microbial activities in long-term.

CONCLUSIONS

The proposed testing protocol is suitable to evaluate long-term performance of an antimicrobial paint by analyzing its microbial activity in large-scale field tests. The WO_x paint shows long-term effectiveness in reducing microbial activities on wall surfaces in both indoor and semi-outdoor environments.

Effect of Ag doped MnO2 nanostructures suitable for wastewater treatment and other environmental pollutant applications

A modest sol-gel method has been employed to prepare the pure and Ag doped MnO2 nanoparticles and methodologically studied their physical, morphological, and photosensitive properties through XRD, TEM, EDAX, Raman, UV, PL and N2 adsorption - desorption study. Tetragonal crystalline arrangement with spherical nanoparticles was found out through XRD and TEM studies. The EDAX studies further supported that formation Ag in the MnO2 crystal matrix. The bandgap energy of Ag doped MnO2 was absorbed through UV spectra. Photo -generated recombination process and surface related defects were further recognized by PL spectra. Through visible light irradiation, the photo - degradation of methyl orange (MO) and phenol dye solutions were observed. The optimum condition of (10 wt% of Ag) Ag doped MnO2 catalyst showed tremendous photocatalytic efficiency towards MO than phenol under same experimental study.

Enhanced Fe-TiO2 Solar Photocatalysts on Porous Platforms for Water Purification

In this study, polyethylene glycol-modified titanium dioxide (PEG-modified TiO2) nanopowders were prepared using a fast solvothermal method under microwave irradiation, and without any further calcination processes. These nanopowders were further impregnated on porous polymeric platforms by drop-casting. The effect of adding iron with different molar ratios (1, 2, and 5%) of iron precursor was investigated. The characterization of the produced materials was carried out by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Optical characterization of all the materials was also carried out. SEM showed that pure TiO2 and Fe-TiO2 nanostructures presented similar nanosized and spherical particles, which uniformly covered the substrates. From XRD, pure TiO2 anatase was obtained for all nanopowders produced, which was further confirmed by Raman spectroscopy on the impregnated substrates. XPS and UV-VIS absorption spectroscopy emission spectra revealed that the presence of Fe ions on the Fe-TiO2 nanostructures led to the introduction of new intermediate energy levels, as well as defects that contributed to an enhancement in the photocatalytic performance. The photocatalytic results under solar radiation demonstrated increased photocatalytic activity in the presence of the 5% Fe-TiO2 nanostructures (Rhodamine B degradation of 85% after 3.5 h, compared to 74% with pure TiO2 for the same exposure time). The photodegradation rate of RhB dye with the Fe-TiO2 substrate was 1.5-times faster than pure TiO2. Reusability tests were also performed. The approach developed in this work originated novel functionalized photocatalytic platforms, which were revealed to be promising for the removal of organic dyes from wastewater.

Synthesis and Photocatalytic Activity of Hexagonal Plate-like Shaped Au Nanoparticles/ZnO Composite Particles under Visible-light Irradiation

We synthesized Au nanoparticle (AuNP)/ZnO composite particles in presence of an anionic surfactant and evaluated their photocatalytic activity under visible-light irradiation. AuNPs synthesized from HAuCl₄ in the presence of amylase and the precursor solutions of ZnO were mixed, followed by a hydrothermal process, to synthesize crystal face-controlled AuNP/ZnO composite particles. X-ray diffraction (XRD) patterns and ultraviolet-visible (UV-Vis) spectra confirmed the formation of AuNP/ZnO composite particles. Furthermore, different Au to Zn concentration ratios in the precursor solutions resulted in different amounts of AuNPs in the composite particles. In addition, the average size of the AuNP/ZnO composite particles decreased with increasing Au to Zn concentration ratio. We believe AuNPs act as the nuclei for ZnO particle formation. The photocatalytic activity of the AuNP/ZnO composite particles was evaluated by the photodegradation of methylene blue (MB) under visible-light irradiation. The photodegradation rate of MB was higher with AuNP/ZnO composite particles compared to that with the ZnO particles synthesized in the absence of AuNPs. The AuNP/ZnO composite particles exhibit photocatalytic activity under visible-light irradiation owing to the enhanced charge separation efficiency and the localized surface plasmon resonance effect.

Hydrothermal carbonation carbon-based photocatalysis under visible light: Modification for enhanced removal of organic pollutant and novel insight into the photocatalytic mechanism

Hydrothermal carbonation carbon (HTCC) is emerging as a promising alternative for photocatalytic removal of contaminants from water. However, the catalytic activity of HTCC is limited by its poor charge transfer ability, and its photocatalytic mechanism remains unclear. Herein, a unique photosensitization-like mechanism was firstly found on Fe modified HTCC (Fe-HTCC) derived from glucose for effective removal of organic pollutants. Under visible light illumination, the organic pollutant coordinated with Fe-HTCC enabled electrons transfer from its highest occupied molecular orbital (HOMO) to conduction band (CB) of Fe-HTCC, which not only oxidized pollutant itself, but also generated oxygen-centered radical for reducing O₂ into O₂^•- towards pollutant removal. The degradation kinetic constant of sulfamethoxazole (SMX) over Fe-HTCC was about 1024.4 and 20.5 times higher than that of HTCC and g-C₃N₄, respectively. The enhanced performance of Fe-HTCC was originated from dual role of Fe modification: one is to boost the electron-deficient C sites which prefer to coordinate with amino or hydroxyl of pollutants; the other is to enhance the linkage of discrete polyfuran chains in Fe-HTCC for effective electron transfer from pollutant to Fe-HTCC. This work provides new insight into the synthesis and mechanism of HTCC-based high-efficiency photocatalyst for water decontamination.

A critical review on N-modified TiO2 limits to treat chemical and biological contaminants in water. Evidence that enhanced visible light absorption does not lead to higher degradation rates under whole solar light

Intensive research has been focused on the synthesis of N-modified TiO₂ materials having visible light absorption in order to get higher solar photocatalytic degradation rates of pollutants in water. However, an exhaustive revision of the topic underlines several controversial issues related to N-modified TiO₂ materials; these issues concern (a) the methodology used for preparation, (b) the assessment of the structural characteristics, (c) the mechanistic action modes and (d) the raisons argued to explain the limited performances of the prepared materials for organic and biological targets photodegradation in water. Taking advantage of last year's progress in analytical chemistry and in material characterization methods, the authors show, for example, that some works in the literature controversially attribute the term nitrogen doping without enough analytical evidence. Additionally, some papers describe N-modified TiO₂ photocatalysts as being able to generate holes with enough oxidative potential to form hydroxyl radicals under visible light. This last assertion often derives from a no pertinent use of illumination sources, light filters, or targets or a limited understanding of the thermodynamic aspects of the studied systems. None of N-containing materials prepared by herein presented methods leads, under solar light, to a significant enhancement in pollutants degradation and microorganism's inactivation kinetics.

Development of Gold Nanoparticle-Based SERS Substrates on TiO2-Coating to Reduce the Coffee Ring Effect

Hydrophilic surface-enhanced Raman spectroscopy (SERS) substrates were prepared by a combination of TiO₂-coatings of aluminium plates through a direct titanium tetraisopropoxide (TTIP) coating and drop coated by synthesised gold nanoparticles (AuNPs). Differences between the wettability of the untreated substrates, the slowly dried Ti(OH)₄ substrates and calcinated as well as plasma treated TiO₂ substrates were analysed by water contact angle (WCA) measurements. The hydrophilic behaviour of the developed substrates helped to improve the distribution of the AuNPs, which reflects in overall higher lateral SERS enhancement. Surface enhancement of the substrates was tested with target molecule rhodamine 6G (R6G) and a fibre-coupled 638 nm Raman spectrometer. Additionally, the morphology of the substrates was characterised using scanning electron microscopy (SEM) and Raman microscopy. The studies showed a reduced influence of the coffee ring effect on the particle distribution, resulting in a more broadly distributed edge region, which increased the spatial reproducibility of the measured SERS signal in the surface-enhanced Raman mapping measurements on mm scale.

Titanium dioxide based nanocomposites - Current trends and emerging strategies for the photocatalytic degradation of ruinous environmental pollutants

Many ruinous pollutants are omnipresent in the environment and among them; pesticides are xenobiotic and pose to be a bio-recalcitrance. Their detrimental ecological and environmental impacts attract attention of environmental excerpts and the surge of stringent regulations have endows the need of a technically feasible treatment. This critical review emphasizes about the occurrence, abundance and fate of structurally distinct pesticides in different environment. The practiced remedial strategies and in particular, the advanced oxidation processes (AOPs) those utilize the photo-catalytic properties of nano-composites for the degradation of pollutants are critically discussed. Photo-catalytic degradation utilizes many composite materials at nano-scale level, wherein synthesis of nano-composites with appropriate precursors and other adjoining functional moieties are of prime importance. Therefore, suitable starter materials along with the reaction conditions are prerequisite for effectively tailoring the nano-composites. The aforementioned aspects and their customized applications are critically discussed. The associated challenges, opportunities and process economics of degradation using photo-catalytic AOP techniques are highlighted and in addition, the review tries to explain how best the photo-degradation can be a stand-alone tool with a societal importance. Conclusively, the future prospects for undertaking new researches in photo-catalytic breakdown of pollutants that can be judiciously sustainable.

Conducting polymers/zinc oxide-based photocatalysts for environmental remediation: a review

The accessibility to clean water is essential for humans, yet nearly 250 million people die yearly due to contamination by cholera, dysentery, arsenicosis, hepatitis A, polio, typhoid fever, schistosomiasis, malaria, and lead poisoning, according to the World Health Organization. Therefore, advanced materials and techniques are needed to remove contaminants. Here, we review nanohybrids combining conducting polymers and zinc oxide for the photocatalytic purification of waters, with focus on in situ polymerization, template synthesis, sol-gel method, and mixing of semiconductors. Advantages include less corrosion of zinc oxide, less charge recombination and more visible light absorption, up to 53%.

A light-heat synergism in the sub-bandgap photocatalytic response of pristine TiO2: a study of in situ diffusion reflectance and conductance

Pristine TiO₂ materials are mainly used as photocatalysts under super-bandgap light illumination. The sub-bandgap (SBG) photocatalytic response has seldom been investigated and the mechanism of action remains unclear. In the current research, we firstly study the SBG light electronic transition of pristine P25 TiO₂ by means of in situ diffusion reflectance and (photo)conductance measurements under finely controllable conditions. It is revealed that the SBG light can promote valence band (VB) electrons to the exponentially-distributed gap states of the TiO₂, which can then be thermally activated to the CB states. A hole in the VB and an electron in the CB can be generated by the synergism of a SBG photon and heat. It is also seen that the photoinduced electrons can transfer to O₂ through the CB states, and that the holes can be captured by isopropanol molecules. As a result, isopropanol dehydrogenation can occur over pristine TiO₂ under SBG light illumination. It is seen that the photocatalytic activity increases with temperature and the energy of the SBG photons, in agreement with the light-heat synergistic electric transition via the exponential gap states. The present research reveals a mechanism for the SBG light photocatalytic response of pristine TiO₂ materials, which is important in designing highly-active visible light active photocatalysts.

Antimicrobial Activity of Commercial Photocatalytic SaniTise™ Window Glass

Photocatalytic and antibacterial properties of TiO2-based SaniTise™ glass by Pilkington were studied with an aim to benchmark this first commercial UVA-activated antimicrobial glass and to evaluate its efficacy in indoor-like conditions. For comparison, the antibacterial and photocatalytic activity of self-cleaning BIOCLEAN® glass and photocatalytically inactive clear float PLANICLEAR® control glass were analysed. The presence of an anatase TiO2 layer was demonstrated on the surface of SaniTise™ and BIOCLEAN®. Photocatalytic degradation of organic model dye and antibacterial activity against Escherichia coli and Staphylococcus aureus were higher on SaniTise™ than on BIOCLEAN®. In a liquid antibacterial assay corresponding to ISO 27447 format, 4h exposure of bacteria to the SaniTise™ surface under UVA resulted in >2.8 log decrease in E. coli and >2.5 log decrease in S. aureus viable cell counts. In experiments with the more application-relevant “dry droplet method”, significantly higher antibacterial activity was observed up to the level where during 4h at ≤50% RH complete inactivation of bacteria was observed also on PLANICLEAR® control glass. The latter raises concerns about the real-life relevancy of the standard test conditions and suggests that at low air humidity conditions, shorter exposure periods than suggested by current antimicrobial testing protocols should be targeted by photocatalytically active antibacterial surfaces.

On the degradation of (micro)plastics: Degradation methods, influencing factors, environmental impacts

Plastics and microplastics are difficult to degrade in the natural environment due to their hydrophobicity, the presence of stable covalent bonds and functional groups that are not susceptible to attack. In nature, microplastics are more likely to attract other substances due to their large specific surface area, which further prevents degradation from occurring. Some of these substances are toxic and harmful, and can be spread to various organisms through the food chain along with the microplastics to cause harm to them. Degradation is an effective way to eliminate plastic pollution, and a comprehensive understanding of the methods and mechanisms of plastic degradation is necessary, because it is the result of synergistic effects of several degradation methods, both in nature and in consideration of future engineering applications. The authors firstly summarize the degradation methods of (micro)plastics; secondly, review the influence of intrinsic properties and environmental factors during the degradation process; finally, discuss the environmental impact of the degradation products of (micro)plastics. It is evident that the degradation of (micro)plastics still has many challenges to overcome, and there are no mature and effective methods that can be applied in engineering practice or widely used in nature. Therefore, there is an urgent need for research on the degradation of (micro)plastics.

Evaluation of photodegradation performance by paper microzones

Currently, the performance evaluation of catalysts usually requires expensive instruments. Hence, it is imperative to develop an alternative, green and sustainable method to investigate the photocatalytic reaction processes. Herein, the variation of degradation performance of different wastewaters with different dosage of P25 TiO₂ was evaluated to verify the reliability of the paper microzones method (PMZs). The optimum P25 TiO₂ dosage of 1 g/L for the degradation of methylene blue (MB) (UV light for 6 mins) and 0.5 g/L for the degradation of fuchsin basic (FB) (UV light for 5 mins) was obtained by the PMZs method. For the photocatalytic degradation of trivalent iron ion complexed salicylic acid (Fe(III)-SA) solution, the R² values of 0.904 and 0.801 were obtained for the photocatalytic reaction kinetics by PMZs and spectrophotometry, respectively, which again indicated the high reliability of PMZs. The accuracy of the results obtained by PMZs method relative to the spectrophotometric method ranged from 68.80% to 87.54% when degrading MB, FB, mixture of MB and FB, and Fe(III)-SA by P25 TiO₂. Therefore, the PMZs method is all in line with the requirements of low-carbon environmental protection and green chemistry, and has broad application prospects in the future.

A Simple Preparation Method of Graphene and TiO2 Loaded Activated Carbon Fiber and Its Application for Indoor Formaldehyde Degradation

Formaldehyde has a significant impact on human health. This study used a simple dipping method to load graphene-titanium dioxide (GR-TiO2) on activated carbon fibers (ACFs). The microstructure of GR-TiO2/ACF hybrid material was observed by SEM, combined with XRD and BET analysis. The result showed that the GR-TiO2/ACF hybrid material had a specific surface area of 893.08 m2/g and average pore size of 2.35 nm. The formaldehyde degradation efficiency of the prepared material was tested under different conditions, such as ultraviolet (UV) radiation, air supply volume, relative humidity, initial mass concentration. The results showed that the UV radiation intensity, airflow and the initial mass concentration were positively correlated with the formaldehyde removal rate, and the relative humidity was negatively correlated with the formaldehyde removal rate. The GR-TiO2/ACF hybrid material had a maximum formaldehyde removal rate of 85.54% within 120 min.

Enhanced Photocatalytic Activity and Stability of Bi2WO6 - TiO2-N Nanocomposites in the Oxidation of Volatile Pollutants

The development of active and stable photocatalysts for the degradation of volatile organic compounds under visible light is important for efficient light utilization and environmental protection. Titanium dioxide doped with nitrogen is known to have a high activity but it exhibits a relatively low stability due to a gradual degradation of nitrogen species under highly powerful radiation. In this paper, we show that the combination of N-doped TiO2 with bismuth tungstate prevents its degradation during the photocatalytic process and results in a very stable composite photocatalyst. The synthesis of Bi2WO6-TiO2-N composites is preformed through the hydrothermal treatment of an aqueous medium containing nanocrystalline N-doped TiO2, as well as bismuth (III) nitrate and sodium tungstate followed by drying in air. The effect of the molar ratio between the components on their characteristics and photocatalytic activity is discussed. In addition to an enhanced stability, the composite photocatalysts with a low content of Bi2WO6 also exhibit an enhanced activity that is substantially higher than the activity of individual TiO2-N and Bi2WO6 materials. Thus, the Bi2WO6-TiO2-N composite has the potential as an active and stable photocatalyst for efficient purification of air.

Development and Functionalization of Visible-Light-Driven Water-Splitting Photocatalysts

With global warming and the depletion of fossil resources, our fossil fuel-dependent society is expected to shift to one that instead uses hydrogen (H2) as a clean and renewable energy. To realize this, the photocatalytic water-splitting reaction, which produces H2 from water and solar energy through photocatalysis, has attracted much attention. However, for practical use, the functionality of water-splitting photocatalysts must be further improved to efficiently absorb visible (Vis) light, which accounts for the majority of sunlight. Considering the mechanism of water-splitting photocatalysis, researchers in the various fields must be employed in this type of study to achieve this. However, for researchers in fields other than catalytic chemistry, ceramic (semiconductor) materials chemistry, and electrochemistry to participate in this field, new reviews that summarize previous reports on water-splitting photocatalysis seem to be needed. Therefore, in this review, we summarize recent studies on the development and functionalization of Vis-light-driven water-splitting photocatalysts. Through this summary, we aim to share current technology and future challenges with readers in the various fields and help expedite the practical application of Vis-light-driven water-splitting photocatalysts.

Synthetic Fuels from Biomass: Photocatalytic Hydrodecarboxylation of Octanoic Acid by Ni Nanoparticles Deposited on TiO2

Decarboxylation of low-value fatty acids from biomass is a simple process to produce synthetic fuels suitable to be blended with gasoline or diesel. The present study reports the photocatalytic decarboxylation of octanoic acid in the presence of H₂ by a series of modified TiO₂ to form mixtures of n-heptane and tetradecane as major products in variable proportions, depending on the photocatalyst and the reaction conditions. It was found that the photocatalytic activity increases upon an optimal reductive NaBH₄ treatment, presumably by generation of surface oxygen vacancies and by the deposition of Ni nanoparticles in the appropriate loading. Under the optimized conditions, an almost complete octanoic acid conversion and a combined selectivity to n-heptane and tetradecane over 80 % were reached at 10 h of UV/Vis light irradiation with a 300 W Xe lamp. No changes in the photocatalytic performance were observed for six consecutive runs. The present results illustrate the possibility that photocatalytic decarboxylation offers for the transformation of biomass into synthetic fuels under mild conditions.

Enhanced Photocatalytic Activity of Hierarchical Bi2WO6 Microballs by Modification with Noble Metals

Visible-responsive photocatalysts for environmental purification and fuel generation are, currently, highly sought after. Among the possible candidates, Bi2WO6 (BWO) has been considered due to its efficient light harvesting, stability, and promising activities. Here, hierarchical BWO microballs have been prepared using a hydrothermal method, and additionally modified with deposits of noble metals (gold, silver, copper, palladium and platinum) by the photodeposition method. The structure, morphology, photoabsorption properties, and surface composition of bare and metal-modified BWO samples were investigated by XRD, SEM, DRS and XPS analyses. The photocatalytic activity was evaluated by the oxidative degradation of model dye (methyl orange (MO)) under UV/vis, and hydrogen generation under vis and/or UV irradiation. It was found that hierarchical morphology is detrimental for high photocatalytic activity in both tested systems, resulting in the improved degradation of MO (ca. 65% during 90 min of UV/vis irradiation), and hydrogen evolution (0.1 and 0.4 μmol h−1 under vis and UV/vis irradiation, respectively). Moreover, the type of noble metal and its properties influence the overall photocatalytic performance. It was found that, under UV/vis irradiation, only platinum accelerates hydrogen evolution, whereas under vis irradiation the activity follows the order: BWO < BWO/Cu < BWO/Ag < BWO/Pt < BWO/Pd < BWO/Au. It was concluded that zero-valent metal is recommended for high vis response, probably due to plasmonic photocatalysis, efficient light harvesting ability, and co-catalytic role.

Sustainable Green Nanotechnologies for Innovative Purifications of Water: Synthesis of the Nanoparticles from Renewable Sources

Polluting the natural water resources is a serious global issue, which is confirmed by the fact that today at least 2 billion people consume water from contaminated sources. The conventional wastewater treatment methods cannot effectively remove the persistent pollutants (e.g., drugs, organic dyes, pesticides) from the aqueous environment. Heterogeneous photocatalysis is a promising and sustainable alternative for water remediation. It is based on the interaction between light irradiation and the semiconductors (e.g., TiO₂, ZnO) as photocatalysts, but these compounds, unfortunately, have some disadvantages. Hence, great attention has been paid to the nanotechnology as a possible way of improvement. Nanomaterials have extraordinary properties; however, their conventional synthesis is often difficult and requires a significant amount of dangerous chemicals. This concise topical review gives recent updates and trends in development of sustainable and green pathways in the synthesis of nanomaterials, as well as in their application for water remediation. In our review we put emphasis on the eco-friendly, mostly plant extract-based materials. The importance of this topic, including this study as well, is proved by the growing number of publications since 2018. Due to the current serious environmental issues (e.g., global warming, shortage of pure and quality water), it is necessary for the traditional TiO₂ and ZnO semiconductors to be replaced with the harmless, non-toxic, and more powerful nanocomposites as photocatalysts. Not only because of their higher efficiency as compared to the bulk semiconductors, but also because of the presence of biomolecules that can add up to the pollutant removal efficiency, which has been already confirmed in many researches. However, despite the fact that the application of heterogeneous photocatalysis together with green nanotechnology is absolutely the future in water purification, there are some challenges which have to be overcome. The exact effects of the biomolecules obtained from plants in the synthesis of nanoparticles, as well as in the photocatalytic processes, are not exactly known and require further investigation. Furthermore, heterogeneous photocatalysis is a well-known and commonly examined process; however, its practical use outside the laboratory is expensive and difficult. Thus, it has to be simplified and improved in order to be available for everyone. The aim of our review is to suggest and prove that using these bio-inspired compounds it is possible to reduce human footprint in the nature.

Facile synthesis of a nano titanium catalyst and its performance in selective oxidation of aromatic and pyridinic alcohols under visible light

The oxidation of alcohols to the corresponding carbonyl compounds is of great significance in chemical synthesis and fine chemical production.

Photocatalytic degradation-based efficient elimination of pesticides using ruthenium/gold metal nanoparticle-anchored zirconium dioxide

Ruthenium and gold metal nanoparticles-incorporated zirconium dioxide (ZrO2@Ru and ZrO2@Au) nanostructures were developed as promising photocatalysts for wastewater remediation.

Mechanochemical synthesis of ternary heterojunctions TiO2(A)/TiO2(R)/ZnO and TiO2(A)/TiO2(R)/SnO2 for effective charge separation in semiconductor photocatalysis: A comparative study

TiO₂, ZnO, and SnO₂ metal oxides were synthesized by the sol-gel method and heterojunctions were fabricated by combining TiO₂ with either ZnO or SnO₂ in a 1:1 ratio using mechanochemical ball milling process. The ball milling process promotes phase transition of TiO₂ from anatase to rutile and yields ternary heterojunction of the type TiO₂(A)/TiO₂(R)/ZnO and TiO₂(A)/TiO₂(R)/SnO₂ (A-anatase and R-rutile). These ternary heterojunctions were characterized by various analytical techniques and its photocatalytic efficiency is evaluated using 4-Chloro Phenol as a model compound under UV and solar light. The enhanced catalytic activity of TiO₂(A)/TiO₂(R)/ZnO heterojunction is attributed to the formation of Ti³⁺-V_o defect states which leads to the efficient charge carrier separation. During the ball milling process severe crystal deformation takes place in TiO₂ and ZnO lattices by creating crystal lattice distortion which leads to the formation of defects due to valency mismatch between Ti⁴⁺ and Zn²⁺. A mechanistic pathway is proposed for the enhanced photocatalytic activity of the ternary heterojunctions.

TiO2 nanocrystal rods on titanium microwires: growth, vacuum annealing, and photoelectrochemical oxygen evolution

Titania nanocrystal rods grown hydrothermally onto titanium microwire are mechanically robust and photoelectrochemically active.

Direct dye wastewater photocatalysis using immobilized titanium dioxide on fixed substrate

Photocatalysis is a promising technology that can be applied to the dyeing of wastewater. During the process of photocatalysis, titanium dioxide (TiO₂) is often used as a catalyst due to its low cost and broad availability. However, the use of TiO₂ powders can result in certain difficulties associated with separating TiO₂ from the treated wastewater. Therefore, immobilization of TiO₂ on two different substrates, including glass and iron beads, was studied in this body of research work. The composite materials were prepared by spraying liquid dispersion onto the substrates, and the materials were then calcined at different temperatures (600-750 °C). At 700 °C calcination temperature, SEM and EDS analyses revealed that the particles of TiO₂ were evenly distributed on the substrates. Importantly, the deposited TiO₂ particles are mixed-phase anatase and rutile structures, both of which are considered beneficial to the photocatalysis process. Ultimately, a degree of direct dye photodegradation efficiency of 64.0 % at 4 h was achieved from the composite materials that were calcined at 700 °C. The degradation efficiency of the reused catalyst was not significantly changed in the second cycle revealing their capability in reusable. The stability of immobilized TiO₂ onto the fixed substrates was still high after the second use.

Facile solvothermal synthesis of plate-like submicron NaNbO3 particles

Platy particles of NaNbO3 were successfully prepared by a solvothermal reaction using a methanol/ethanol mixed solvent, in contrast to the formation of cubic NaNbO3 particles from methanol alone.

Boosting charge migration in V2O5 nanorods by niobium doping for enhanced photocatalytic activity

Niobium dopants have improved the structural and optoelectronic properties of V2O5 nanorods, resulting in enhanced charge kinetics for photocatalytic and photoelectrochemical activity.

Preparation of InP quantum dots-TiO2 nanoparticle composites with enhanced visible light induced photocatalytic activity

Environmentally friendly InP-based quantum dots (QDs) are expected to be ideal visible-light-harvesting materials because of their unique photophysical properties. Herein, we report on the results of using a combination of...

Vertically Aligned Nanorods Fe2TiO5 and Coupling of NiMoO4/CoMoO4 as A Hole-Transfer Cocatalyst for Enhancing Photoelectrochemical Water Oxidation Performance

Fe2TiO5, a promising photoanode material for photoelectrochemical (PEC) splitting water, was limited by its poor conductivity and short carrier diffusion length. Herein, a novel Fe2TiO5 nanorods with the new cocatalyst...