Surface modification of TiO2 photocatalyst for environmental applications

Peroxymonosulfate activation by black TiO2 nanotube arrays under solar light: Switching the activation mechanism and enhancing catalytic activity and stability

Black TiO₂ nanotube arrays (black TNAs) suffer from the low activity and deactivation for peroxymonosulfate (PMS) activation, which limit their application in the oxidative destruction of organic pollutants in water. Here, we report an efficient, environmentally benign, and cost-effective method to enhance the catalytic activity and prevent the deactivation of black TNAs in PMS activation by utilizing solar energy. Optical absorption and electrochemical analysis and density functional theory calculations demonstrated that abundant oxygen vacancies (estimated to be 26%) on the black TNAs surface markedly improved solar light absorption and electrical conductivity and played a critical role as a catalytic active site for PMS activation. As a result, the solar light-irradiated black TNAs/PMS system exhibited the higher phenol degradation rate (k = 0.0488 min^-1) and total organic carbon (TOC) removal efficiency (~70%) compared to other TNAs systems. These results were ascribed to the switching of the reaction mechanism from non-radical mechanism to radical-involved. Black TNAs oxidized organic pollutants by mediating electron transfer from organics to PMS in the dark (i.e., a non-radical pathway). On the other hand, PMS activation under solar light irradiation involved the production of highly reactive sulfate and hydroxyl radicals (i.e., radical pathway), markedly improving the degradation and mineralization of organics. Additionally, the solar light-irradiated black TNAs showed relative pH-independence for PMS activation and durable catalytic performance without the loss of activity during the repetitive reaction cycles.

Photocatalytic degradation of gaseous benzene using metal oxide nanocomposites

Rapid industrial growth has been accompanied by the pollution of hazardous volatile organic pollutants (VOCs) in air. Among various options available for the treatment of VOCs, the use of metal oxide composites as photocatalysts has been adopted preferably due to their potential to induce the synergistic interactions between the metal nanoparticles (NPs) and metal oxides (especially titanium dioxide (TiO₂)). In this context, an in-depth review is offered to describe the fundamental mechanism of metal oxide-based photocatalysis for the oxidation of gaseous benzene as a model VOC. The discussion has been extended further to evaluate their performances in terms of key performance metrics (e.g., quantum yield (QY), space-time yield (STY), and figure of merit (FOM)). The TiO₂-based metallic bi-component photocatalysts (e.g., Sr₂CeO₄/TiO₂) generally exhibited better photodegradation efficiency with enhanced light absorption capability than monometallic-TiO₂ (e.g., Pd-TiO₂) composites or other modified photocatalysts (e.g., metal-organic framework (MOF)-based composites). Finally, we address the current challenges and future perspectives in this highly challenging research field.

Photoactive Materials for Decomposition of Organic Matter Prior to Water Analysis—A Review Containing Original Research

Water plays a fundamental role in meeting the basic needs of society. Surface waters contain numerous organic pollutants, such as pesticides, drugs, and surfactants. The use of photolysis processes in organic matter degradation not only has practical applications in wastewater treatment but is also of major importance in the pretreatment of samples prior to the trace analysis of numerous analytes. The heterogeneous degradation is simple to implement prior to ultra-traces determination and is the only one allowed before the speciation analysis. Speciation analysis is currently the most important environmental challenge. The analysis of water, including tests associated with wastewater pretreatment and the monitoring of aqueous ecosystems, is the largest segment of environmental analysis. In the trace analysis of water, organic compounds are the principal interfering compounds reducing the quality of the obtained results or even preventing the determination of the examined analytes altogether. Some analytical techniques do not perform well in the presence, for example, of surfactants, so mineralization is sometimes required. Advanced oxidation processes are used to remove interfering organic compounds. The oxidation can be performed using homogenous photolysis (UV mineralization with hydrogen peroxide addition), while heterogenous photolysis using semiconductors helps to increase the removal efficiency of interferents dissolved in water. Utilizing semiconductor nanostructured materials as photocatalysts has been shown to be effective for the adequate removal of a wide spectrum of pollutants in water. Several semiconductor systems are used in the degradation of organic compounds, e.g., TiO2, Fe3O4, WO3, Fe2O3, ZnO, and mixtures of these oxides enriched with various precious metals, such as silver or gold. It is very challenging to manage the selectivity and reduction power so that organic compounds can be degraded but without disturbing the speciation of As, Cr, or Tl. Chemical modification of samples and the selection of semiconductor layers, light wavelength, and pH allow for the targeted degradation of specific compounds but may also indirectly affect the analysis of water samples. This review is a presentation of the state of the art of photocatalysis as a simple and effective technique for sample pretreatment in ultra-trace and speciation analysis and its critical as well as unpublished data related to this topic.

Molybdenum Modified Sol–Gel Synthesized TiO2 for the Photocatalytic Degradation of Carbamazepine under UV Irradiation

Pharmaceutical CEC compounds are a potential threat to man, animals, and the environment. In this study, a sol–gel-derived TiO2 (SynTiO2) was produced and subsequently sonochemically doped with a 1.5 wt% Mo to obtain the final product (Mo (1.5 wt%)/SynTiO2). The as-prepared materials were characterized for phase structure, surface, and optical properties by XRD, TEM, N2 adsorption–desorption BET isotherm at 77 K, and PSD by BJH applications, FTIR, XPS, and UV-Vis measurements in DRS mode. Estimated average crystallite size, particle size, surface area, pore-volume, pore size, and energy bandgap were 16.10 nm, 24.55 nm, 43.30 m2/g, 0.07 cm3/g, 6.23 nm, and 3.05 eV, respectively, for Mo/SynTiO2. The same structural parameters were also estimated for the unmodified SynTiO2 with respective values of 14.24 nm, 16.02 nm, 133.87 m2/g, 0.08 cm3/g, 2.32 nm, and 3.3 eV. Structurally improved (Mo (1.5 wt%)/SynTiO2) achieved ≈100% carbamazepine (CBZ) degradation after 240 min UV irradiation under natural (unmodified) pH conditions. Effects of initial pH, catalyst dosage, initial pollutant concentration, chemical scavengers, contaminant ions, hydrogen peroxide (H2O2), and humic acid (HA) were also investigated and discussed. The chemical scavenger test was used to propose involved photocatalytic degradation process mechanism of CBZ.

Preparation and Characterization of Supported Molybdenum Doped TiO2 on α-Al2O3 Ceramic Substrate for the Photocatalytic Degradation of Ibuprofen (IBU) under UV Irradiation

TiO2-based photocatalyst materials have been widely studied for the abatement of contaminants of emerging concerns (CECs) in water sources. In this study, 1.5 wt% Mo-doped HRTiO2 was obtained by the sonochemical method. The material was analyzed and characterized for thermal, structural/textural, morphological, and optical properties using TGA-DSC, XRD, TEM, FTIR, XPS, SEM-EDS, BET (N2 adsorption-desorption measurement and BJH application method), and UV-Vis/DRS measurement. By the dip-coating technique, ~5 mg of Mo/HRTiO2 as an active topcoat was deposited on ceramic. In suspension and for photocatalyst activity performance evaluation, 1 g/L of 1.5 wt% (Mo)/HRTiO2 degraded ~98% of initial 50 mg/L IBU concentration after 80 min of 365 nm UV light irradiation and under natural (unmodified) pH conditions. Effects of initial pH condition, catalyst dosage, and initial pollutant concentration were also investigated in the photocatalyst activity performance in suspension. The photocatalyst test on the supported catalyst removed ~60% of initial 5mg/L IBU concentration, while showing an improved performance with ~90% IBU removal employing double and triple numbers of coated disk tablets. After three successive cycle test runs, XRD phase reflections of base TiO2 component of the active photocatalyst supported layer remained unchanged: An indication of surface coat stability after 360 min of exposure under 365 nm UV irradiation.

4-Mercaptobenzoic Acid Adsorption on TiO2 Anatase (101) and TiO2 Rutile (110) Surfaces

The adsorption of 4-mercaptobenzoic acid (4-MBA) on anatase (101) and rutile (110) TiO2 surfaces has been studied using synchrotron radiation photoelectron spectroscopy and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy techniques. Photoelectron spectroscopy results suggest that the 4-MBA molecule bonds to both TiO2 surfaces through the carboxyl group, following deprotonation in a bidentate geometry. Carbon K-edge NEXAFS spectra show that the phenyl ring of the 4-MBA molecule is oriented at 70° ± 5° from the surface on both the rutile (110) and anatase (101) surfaces, although there are subtle differences in the electronic structure of the molecule following adsorption between the two surfaces.

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.

Light Promotes the Immobilization of U(VI) by Ferrihydrite

The environmental behaviors of uranium closely depend on its interaction with natural minerals. Ferrihydrite widely distributed in nature is considered as one main natural media that is able to change the geochemical behaviors of various elements. However, the semiconductor properties of ferrihydrite and its impacts on the environmental fate of elements are sometimes ignored. The present study systematically clarified the photocatalysis of U(VI) on ferrihydrite under anaerobic and aerobic conditions, respectively. Ferrihydrite showed excellent photoelectric response. Under anaerobic conditions, U(VI) was converted to U(IV) by light-irradiated ferrihydrite, in the form of UO2+x (x < 0.25), where •O2− was the dominant reactive reductive species. At pH 5.0, ~50% of U(VI) was removed after light irradiation for 2 h, while 100% U(VI) was eliminated at pH 6.0. The presence of methanol accelerated the reduction of U(VI). Under aerobic conditions, the light illumination on ferrihydrite also led to an obvious but slower removal of U(VI). The removal of U(VI) increased from ~25% to 70% as the pH increased from 5.0 to 6.0. The generation of H2O2 under aerobic conditions led to the formation of UO4•xH2O precipitates on ferrihydrite. Therefore, it is proved that light irradiation on ferrihydrite significantly changed the species of U(VI) and promoted the removal of uranium both under anaerobic and aerobic conditions.

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.

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.

Preparation and characterization of a self-dispersed and reactive TiO2/BiOBr photocatalyst for self-cleaning and ultraviolet resistant cotton fabrics

A novel and efficient approach is presented herein to develop self-cleaning and ultraviolet resistant cotton fabrics loaded with a self-dispersed and reactive TiO2/BiOBr photocatalyst.

In situ decomposition of bromine-substituted catechol to increase the activity of titanium dioxide catalyst for visible-light-induced aerobic conversion of toluene to benzaldehyde

Surface-modified TiO2 generated by the photolysis of tetrabromocatechol showed higher activity than bare TiO2 in visible-light-induced photocatalytic toluene oxidation.

Switching of Electron Transport Direction from the Long Axis to Short Axis in a Radial SnO2(Head)-Rutile TiO2 Nanorod(Tail) Heteromesocrystal Photocatalyst

Heteroepitaxial growth of rutile TiO₂ nanorods from SnO₂ seeds yielded radial heteromesocrystals consisting of SnO₂(head) and rutile TiO₂ nanorod(tail) with the SnO₂(head) oriented toward the center (TiO₂-NR//SnO₂ HEMCs). Iron oxide clusters were formed on the surface by the chemisorption-calcination technique. The FeO_x-surface modification gives rise to drastic increases in the photocatalytic activity for aerobic oxidation of 2-naphthol under irradiation of UV and visible light. As a 2D-model for 3D-TiO₂-NR//SnO₂ HEMC, electrochemical measurements were performed for the rutile TiO₂-NR array formed on a fluorine-doped tin oxide (SnO₂:F) electrode. The results showed that the FeO_x clusters possess electrocatalytic activity for a multielectron oxygen reduction reaction, and the high photocurrent of the electrode is remarkably reduced by the FeO_x-surface modification. Consequently, the striking photocatalytic activity of FeO_x/TiO₂-NR//SnO₂ HEMCs was ascribable to the switching of the electron transport direction necessary for the charge separation from the long axis of the TiO₂ NR to the short axis.

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.

Radial TiO2 Nanorod-Based Mesocrystals: Synthesis, Characterization, and Applications

Radial TiO2 nanorod-based mesocrystals (TiO2-NR MCs) or so-called “sea-urchin-like microspheres” possess not only attractive appearance but also excellent potential as photocatalyst and electrode materials. As a new type of TiO2-NR MCs, we have recently developed a radial heteromesocrystal photocatalyst consisting of SnO2(head) and rutile TiO2 nanorods(tail) (TiO2-NR//SnO2 HEMCs, symbol “//” denotes heteroepitaxial junction) with the SnO2 head oriented in the central direction in a series of the studies on the nanohybrid photocatalysts with atomically commensurate junctions. This review article reports the fundamentals of TiO2-NR MCs and the applications to photocatalysts and electrodes. Firstly, the synthesis and characterization of TiO2-NR//SnO2 HEMCs is described. Secondly, the photocatalytic activity of recent TiO2-NR MCs and the photocatalytic action mechanism are discussed. Thirdly, the applications of TiO2-NR MCs and the analogs to the electrodes of solar cells and lithium-ion batteries are considered. Finally, we summarize the conclusions with the possible future subjects.

Advanced Photocatalysts Based on Conducting Polymer/Metal Oxide Composites for Environmental Applications

Photocatalysts provide a sustainable method of treating organic pollutants in wastewater and converting greenhouse gases. Many studies have been published on this topic in recent years, which signifies the great interest and attention that this topic inspires in the community, as well as in scientists. Composite photocatalysts based on conducting polymers and metal oxides have emerged as novel and promising photoactive materials. It has been demonstrated that conducting polymers can substantially improve the photocatalytic efficiency of metal oxides owing to their superior photocatalytic activities, high conductivities, and unique electrochemical and optical properties. Consequently, conducting polymer/metal oxide composites exhibit a high photoresponse and possess a higher surface area allowing for visible light absorption, low recombination of charge carriers, and high photocatalytic performance. Herein, we provide an overview of recent advances in the development of conducting polymer/metal oxide composite photocatalysts for organic pollutant degradation and CO2 conversion through photocatalytic processes.

First X-ray Spectroscopic Observations of Atmospheric Titanium Species: Size Dependence and the Emission Source

Titanium dioxide (TiO2) in mineral dust is considered as one of the driving forces of photocatalytic reaction at the aerosol surface in the atmosphere. As a precursor of mineral dust, soil contains ilmenite (FeTiO3) and titanite (CaSiTiO5), which have lower photochemical reactivities than TiO2. However, Ti species other than TiO2 in aerosol particles are not well recognized due to the lack of observation in ambient samples. In this study, Ti species in size-fractionated aerosol samples collected in the Noto Peninsula, Japan, were determined by macroscopic and semi-microscopic X-ray absorption fine structure spectroscopy. Regardless of aerosol particle size, Ti species were primarily composed of rutile, anatase, ilmenite, and titanite. Semi-microscopic Ti speciation showed that Ti-poor spots associated with mineral dust were composed of a mixture of rutile, anatase, ilmenite, and titanite, and Ti-rich spots were primarily composed of TiO2 (rutile or anatase) derived from authigenic minerals or anthropogenic materials. Thus, the Ti species in aerosol particles, especially mineral dust, were not composed solely of TiO2 polymorphs. Therefore, the photochemical reactivities of Ti in aerosol particles may be overestimated when laboratory experiments or model studies employ TiO2 as the representative Ti species.

Mutual influence of cupric cations and several anions in anatase and rutile TiO2 photocatalysis

Copper ions in aqueous solution are known to promote organic oxidation in semiconductor photocatalysis, but the counter anions seem to be important as well. In this work, the performance of Cu(ClO₄)₂ in presence of several anions in sodium forms (F^-, Cl^-, ClO₄^-, NO₃^-, and SO₄^2-) has been examined. Phenol oxidation in aqueous solution (pH 4) under UV light was used as model reaction and TiO₂ in the forms of anatase (AT) and rutile (RT) as photocatalysts. On the addition of 0.1-5 mM Cu²⁺, the reactions on AT and RT all increased. On the addition of 1 mM anions, reactions on AT increased by F^-and SO₄^2-, but reactions on RT all decreased. In presence of 3 mM Cu²⁺, however, reactions on AT and RT all decreased by 1 mM anions except NO₃^-. Such anion effects were also observed for H₂ production on AT and RT in presence of Cu²⁺ and 10% methanol. A possible mechanism for the positive and negative anion effects is discussed. This work indicates that the formation of a Cu(II)/Cu(I) complex with anions weakens the positive effect of copper ions on organic oxidation in TiO₂ photocatalysis.

Photocatalytic Degradation of Plastic Waste: A Mini Review

Plastic waste becomes an immediate threat to our society with ever-increasing negative impacts on our environment and health by entering our food chain. Sunlight is known to be the natural energy source that degrades plastic waste at a very slow rate. Mimicking the role of sunlight, the photocatalytic degradation process could significantly accelerate the degradation rate thanks to the photocatalyst that drastically facilitates the photochemical reactions involved in the degradation process. This mini review begins with an introduction to the chemical compositions of the common plastic waste. The mechanisms of photodegradation of polymers in general were then revisited. Afterwards, a few photocatalysts were introduced with an emphasis on titanium dioxide (TiO2), which is the most frequently used photocatalyst. The roles of TiO2 photocatalyst in the photodegradation process were then elaborated, followed by the recent advances of photocatalytic degradation of various plastic waste. Lastly, our perspectives on the future research directions of photocatalytic plastic degradation are present. Herein, the importance of catalytic photodegradation is emphasized to inspire research on developing new photocatalysts and new processes for decomposition of plastic waste, and then to increase its recycling rate particularly in the current pandemic with the ever-increasing generation of plastic waste.

Controlled growth of ultrasmall Cu2O clusters on TiO2nanoparticles by atmospheric-pressure atomic layer deposition for enhanced photocatalytic activity

This work presents a gas-phase approach for the synthesis of Cu₂O/TiO₂powder-based photocatalysts using atomic layer deposition (ALD). The process is carried out in a fluidized bed reactor working at atmospheric pressure using (trimethylvinylsilyl)-hexafluoroacetulacetonate copper(I) as the Cu-precursor and H₂O vapor as the oxidizer. The saturating regime of the chemical reactions and the linear growth of ALD are achieved. In combination with the unsaturated regime, the ALD approach enables the deposition of ultrasmall Cu₂O clusters with average diameters in the range of 1.3-2.0 nm, narrow particle size distributions and tunable Cu₂O loadings on P25 TiO₂nanoparticles. The photocatalytic performance of Cu₂O/TiO₂photocatalysts is investigated by the degradation of organic dyes, including Rhodamine B (RhB), methyl orange, and methylene blue; the results demonstrate that the surface modification of TiO₂nanoparticles by Cu₂O nanoclusters significantly enhances the photocatalytic activity of TiO₂. This is attributed to the efficient charge transfer between Cu₂O and TiO₂that reduces the charge recombination. The photocatalytic reaction mechanism is further investigated for the degradation of RhB, revealing the dominating role of holes, which contribute to both direct hole oxidation and indirect oxidation (i.e. via the formation of hydroxyl radicals). Our approach provides a fast, scalable and efficient process to deposit ultrasmall Cu₂O clusters in a controllable fashion for surface engineering and modification.

Au nanobipyramids with Pt decoration enveloped in TiO2 nanoboxes for photocatalytic reactions

Noble metal nanocrystals and core-shell nanocomposites have attracted particular interest due to their unique optical properties originating from surface plasmon resonance (SPR) and wide applications related to the SPR effect. In this work, we designed and fabricated a new Au-Pt@TiO2 nanocomposite, in which Au nanobipyramids (AuNBPs) decorated with platinum (Pt) clusters were enveloped in mesoporous TiO2 nanoboxes with nanocavities. AuNBPs provide strong SPR absorption and localized field enhancement restricted to the cavities of TiO2 nanoboxes. The Pt nanoclusters decorated on the surface of AuNBPs can effectively modulate the charge movement and energy transfer in the photocatalytic process. The enhanced electric field provides a local thermal effect for the photocatalytic reaction and promotes the injection process of hot electrons which facilitates carrier separation. The nanoboxes with nanocavities can effectively manage the usage of localized energy and provide space for reaction. Under the cooperative effects, the photocatalytic performance was remarkably improved along with durability and stability. For the AuNBP-Pt@TiO2 nanoboxes, the rhodamine-B degradation efficiency was ∼6.5 times that of AuNBP@TiO2 nanoboxes. The mechanism of the photocatalysis process was proposed based on experimental results and simulations. Benefiting from the excellent structure and properties, the obtained nanostructure is a promising candidate in the fields of pollutant degradation and chemical reaction catalysis.

Photocatalytic exoskeleton: Chitin nanofiber for retrievable and sustainable TiO2 carriers for the decomposition of various pollutants

Loading a photocatalytic TiO₂ to organic carriers has been desired for volumetric TiO₂ incorporation, facile retrieval, and sustainable utilization. Traditionally, suspended TiO₂ nanoparticles or its thin film on two-dimensional substrate are popularly fabricated for pollutants decomposition without carriers; due to poor thermomechanical properties of the organic carriers. Herein, a combination of the chitin nanofiber carrier and atomic layer deposition proves relevance for formation of anatase TiO₂ thin layer so that photocatalytic decomposition in three-dimensional surface. Moreover, chitin nanofiber is capable of holding the TiO₂ nanoparticles for multiple cycles of photocatalysis. Those types of TiO₂ show characteristic degradation performance for gaseous (acetaldehyde) and aqueous pollutants (4-chlorophenol and rhodamine B). After catalytic reaction, chitin/TiO₂ is retrievable owing to carrier's robustness even in water without TiO₂ aggregation and loss. This work suggests that chitin-based photocatalyst is applicable to numerous pollutants through chitin's relatively high chemical resistance and stably wedged TiO₂ during photocatalytic reaction.

TiO2 Inverse Opals Modified by Ag Nanoparticles: A Synergic Effect of Enhanced Visible-Light Absorption and Efficient Charge Separation for Visible-Light Photocatalysis

This work reports on the synthesis, characterization, and photocatalytic performance of the TiO2 inverse opal nanostructure (IP-TiO2) and the IP-TiO2 modified by Ag nanoparticles (Ag@IP-TiO2). The IP-TiO2 is fabricated using polystyrene spheres as the template and TiCl4 as the precursor, and the Ag@IP-TiO2 is realized by photoreduction method. The morphological, structural, and optical properties of the materials are investigated by scanning electron microscopy, X-ray diffraction, ultraviolet–visible (UV-VIS) absorption spectroscopy, and photoluminescence spectroscopy. Their photocatalytic performances are studied by the degradation of rifampicin antibiotic under the visible-light irradiation generated by an LED lamp. The results demonstrate that the IP-TiO2 is composed of mesopores arranged in the honeycomb structure and strongly absorbs visible light in the wavelength range of 400–500 nm. This facilitates the visible-light catalytic activity of IP-TiO2, which is further enhanced by the surface modification by Ag nanoparticles. Our studies on the UV-VIS absorption and photoluminescent properties of the materials reveal that the presence of Ag nanoparticles not only enhances the visible-light absorption of IP-TiO2, but also reduces the recombination of photogenerated electrons and holes. These two factors create a synergic effect that causes the enhanced photocatalytic performance of Ag@IP-TiO2.

Facile synthetic routes for photocatalytic Pb3(BTC)2·H2O coordination polymers

Herein, we report on the successful synthesis of photocatalytic Pb3(BTC)2·H2O polymers via different methods including the surfactant-assisted hydrothermal method, ultrasonic method and reflux method. As the crystal growth is subjected to preparation atmosphere, changes in reaction conditions do not alter the crystal structures of products, but vary their morphology. High ultraviolet-light-driven photocatalytic abilities are attributed to the stable Pb3(BTC)2·H2O, and the effective productions of h+ and ˙OH on the catalysts.

Nanoparticulate Double-Heterojunction Photocatalysts Comprising TiO2(Anatase)/WO3/TiO2(Rutile) with Enhanced Photocatalytic Activity toward the Degradation of Methyl Orange under Near-Ultraviolet and Visible Light

Nanoparticulate double-heterojunction photocatalysts comprising TiO_2(Anatase)/WO₃/TiO_2(Rutile) were produced by a sol-gel method. The resulting photocatalysts exhibit clear synergistic effects when tested toward the degradation of methyl orange under both UV and visible light. Kinetic studies indicate that the degradation rate on the best double-heterojunction photocatalyst (10 wt % WO₃-TiO₂) depends mainly on the amount of dye concentration, contrary to pure oxides in which the degradation rate is limited by diffusion-controlled processes. The synergistic effects were confirmed through systematic and careful studies including holes and OH radical formation, X-ray diffraction, electron microscopy, elemental analysis, UV-vis diffuse reflectance spectroscopy, and surface area analysis. Our results indicate that the successful formation of a double heterojunction in the TiO_2(Anatase)/WO₃/TiO_2(Rutile) system leads to enhanced photoactivity when compared to individual oxides and commercial TiO₂ P25.

Metal Oxide-Based Photocatalytic Paper: A Green Alternative for Environmental Remediation

The interest in advanced photocatalytic technologies with metal oxide-based nanomaterials has been growing exponentially over the years due to their green and sustainable characteristics. Photocatalysis has been employed in several applications ranging from the degradation of pollutants to water splitting, CO2 and N2 reductions, and microorganism inactivation. However, to maintain its eco-friendly aspect, new solutions must be identified to ensure sustainability. One alternative is creating an enhanced photocatalytic paper by introducing cellulose-based materials to the process. Paper can participate as a substrate for the metal oxides, but it can also form composites or membranes, and it adds a valuable contribution as it is environmentally friendly, low-cost, flexible, recyclable, lightweight, and earth abundant. In term of photocatalysts, the use of metal oxides is widely spread, mostly since these materials display enhanced photocatalytic activities, allied to their chemical stability, non-toxicity, and earth abundance, despite being inexpensive and compatible with low-cost wet-chemical synthesis routes. This manuscript extensively reviews the recent developments of using photocatalytic papers with nanostructured metal oxides for environmental remediation. It focuses on titanium dioxide (TiO2) and zinc oxide (ZnO) in the form of nanostructures or thin films. It discusses the main characteristics of metal oxides and correlates them to their photocatalytic activity. The role of cellulose-based materials on the systems’ photocatalytic performance is extensively discussed, and the future perspective for photocatalytic papers is highlighted.