A new visible-light photocatalyst: CdS quantum dots embedded mesoporous TiO2

Hierarchically, Low Band Gap Nanohybrid InVO4-CdS Heterojunction for Visible Light-Driven Toxic Organic Dye Degradations

The synthesis of InVO4-CdS heterojunction photocatalysts has been achieved by a novel two-step approach, including a microwave-assisted technique, followed by a moderate hydrothermal method, marking the first successful instance of such a synthesis. X-ray diffraction, field-emission scanning electron microscopy, elemental color mapping, high-resolution transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, Raman analysis, photoluminescence, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller were employed to investigate the crystal structures, surface morphologies and particle sizes, chemical compositions, and optical characteristics of the as-synthesized materials. The research results indicated that the heterojunction InVO4-CdS, as synthesized, consisted of InVO4 microrods with an average size of around 15 nm and cadmium sulfide (CdS) microflowers with a diameter of 1.5 μm. Furthermore, all of the heterojunctions had favorable photoabsorption properties throughout the visible-light spectrum. The photocatalytic efficiency of the samples obtained was thoroughly assessed by the degradation of acid violet 7 (AV 7) under visible light irradiation with a wavelength greater than 420 nm. The photocatalytic efficiency for the decomposition of AV 7 was greatly enhanced in the InVO4-CdS (IVCS) heterojunctions when compared to prepared bare InVO4 and CdS. Additionally, it was observed that the composite material consisting of IVCS 3 wt % InVO4 combined with CdS exhibited the most significant enhancement in catalytic effectiveness for the photodegradation of AV 7 dye. Specifically, the catalytic performance of this composite material was found to be around 69.4 and 76.2 times greater than that of pure InVO4 and CdS, respectively. Furthermore, the experimental procedure including active species trapping provided evidence that h+ and •O2- radicals were the primary active species involved in the photocatalytic reaction process. Additionally, a potential explanation for the improved photocatalytic activity of the InVO4-CdS heterojunction was presented, taking into account the determination of band positions.

Cellulose nanofibril/titanate nanofiber modified with CdS quantum dots hydrogel with 3D porous structure: A stable photocatalytic adsorbent for Cr(VI) removal

A novel cellulose nanofibril/titanate nanofiber modified with CdS quantum dots hydrogel (CTH) was synthesized as an effective, stable, and recyclable photocatalytic adsorbent using cellulose nanofibril (CN), titanate nanofiber (TN), and CdS quantum dots. Within the CTH structure, CN formed an essential framework, creating a three-dimensional (3D) porous structure that enhanced the specific surface area and provided abundant adsorption sites for Cr(VI). Simultaneously, TN modified with CdS quantum dots (TN-CdS) served as a nanoscale Z-type photocatalyst, facilitating the efficient separation of photoinduced electrons and holes, further increasing the photocatalytic efficiency. The morphological, chemical, and optical properties of CTH were thoroughly characterized. The CTH demonstrated the maximum theoretical adsorption capacity of 373.3 ± 14.2 mg/g, which was 3.4 times higher than that of CN hydrogel. Furthermore, the photocatalytic reduction rate constant of the CTH was 0.0586 ± 0.0038 min-1, which was 6.4 times higher than that of TN-CdS. Notably, CTH displayed outstanding stability, maintaining 84.9 % of its initial removal efficiency even after undergoing five consecutive adsorption-desorption cycles. The remarkable performance of CTH in Cr(VI) removal was attributed to its 3D porous structure, comprising CN and TN-CdS. These findings provide novel insights into developing a stable photocatalytic adsorbent for Cr(VI) removal.

Biofunctionalized CdS Quantum Dots: A Case Study on Nanomaterial Toxicity in the Photocatalytic Wastewater Treatment Process

The toxic nature of inorganic nanostructured materials as photocatalysts is often not accounted for in traditional wastewater treatment reactions. Particularly, some inorganic nanomaterials employed as photocatalysts may release secondary pollutants in the form of ionic species that leach out due to photocorrosion. In this context, this work is a proof-of-concept study for exploring the environmental toxicity effect of extremely small-sized nanoparticles (<10 nm) like quantum dots (QDs) that are employed as photocatalysts, and in this study, cadmium sulfide (CdS) QDs are chosen. Typically, CdS is an excellent semiconductor with suitable bandgap and band-edge positions that is attractive for applications in solar cells, photocatalysis, and bioimaging. However, the leaching of toxic cadmium (Cd2+) metal ions due to the poor photocorrosion stability of CdS is a matter of serious concern. Therefore, in this report, a cost-effective strategy is devised for biofunctionalizing the active surface of CdS QDs by employing tea leaf extract, which is expected to hinder photocorrosion and prevent the leaching of toxic Cd2+ ions. The coating of tea leaf moieties (chlorophyll and polyphenol) over the CdS QDs (referred to hereafter as G-CdS QDs) was confirmed through structural, morphological, and chemical analysis. Moreover, the enhanced visible-light absorption and emission intensity of G-CdS QDs in comparison to that of C-CdS QDs synthesized through a conventional chemical synthesis approach confirmed the presence of chlorophyll/polyphenol coating. Interestingly, the polyphenol/chlorophyll molecules formed a heterojunction with CdS QDs and enabled the G-CdS QDs to exhibit enhanced photocatalytic activity in the degradation of methylene blue dye molecules over C-CdS QDs while effectively preventing photocorrosion as confirmed from cyclic photodegradation studies. Furthermore, detailed toxicity studies were conducted by exposing zebrafish embryos to the as-synthesized CdS QDs for 72 h. Surprisingly, the survival rate of the zebrafish embryos exposed to G-CdS QDs was equal to that of the control, indicating a significant reduction in the leaching of Cd2+ ions from G-CdS QDs in comparison to C-CdS QDs. The chemical environment of C-CdS and G-CdS before and after the photocatalysis reaction was examined by X-ray photoelectron spectroscopy. These experimental findings prove that biocompatibility and toxicity could be controlled by simply adding tea leaf extract during the synthesis of nanostructured materials, and revisiting green synthesis techniques can be beneficial. Furthermore, repurposing the discarded tea leaves may not only facilitate the control of toxicity of inorganic nanostructured materials but can also help in enhancing global environmental sustainability.

Ultra-mild synthesis of nanometric metal chalcogenides using organyl chalcogenide precursors

Bis(trialkylsilyl) monochalcogenides and diorganyl dichalcogenides, (R₃Si)₂E and R₂E₂ (E = S, Se or Te and R = alkyl, aryl or allyl group), have emerged in the past decade as excellent reagents for the synthesis of metal chalcogenide nanoparticles (NPs) and clusters owing to their ability to transfer the chalcogenide anion (E^2-) under ultra-mild conditions and versatility in reacting even with non-conventional metal reagents or being employed in a variety of synthetic methods. In comparison, the related non-silylated diorganyl monochalcogenides R₂E have received attention only recently for the solution phase synthesis of metal chalcogenide NPs. In spite of sharing many similarities, these three families of organyl chalcogenides are different in their coordination ability and decomposition behavior, and therefore in reactivities towards metal reagents. This feature article provides a concise overview on the use of these three families as synthons for the ultralow-temperature synthesis of metal chalcogenide nanomaterials, deliberating their different decomposition mechanisms and critically assessing their advantages for certain applications. More specifically, it discusses their usefulness in (i) affording molecular precursors with different kinetic and thermal stabilities, (ii) isolating reactive intermediates for comprehending the mechanism of molecule-to-nanoparticle transformation and, therefore, achieving fine control over the synthesis, (iii) stabilizing isolable metastable or difficult-to-achieve phases, and (iv) yielding complex ternary nanoparticles with controlled stoichiometry or composites with sensitive materials without modifying the characteristics of the latter. Besides providing a perspective on the low-temperature synthesis of nanomaterials, this overview is expected to assist further progress, particularly in the field of R₂E, leading to interesting materials including metastable ones for new applications.

Complete photocatalytic degradation of tetracycline by carbon doped TiO2 supported with stable metal nitrate hydroxide

Visible light-driven carbon-doped TiO₂ supported with metal nitrate hydroxide (CT-Ni/Co/Cu) nanocomposites were prepared and characterized by various studies. It is fascinating to note that particle size of TiO₂ was substantially reduced from 5 μm to 50 nm after doping of carbon which was confirmed by FESEM. Moreover, the incorporation of stable metal (Cu) nitrate hydroxide further enhanced the visible light absorption up to 800 nm as evident by UV-DRS. The carbon doping and copper nitrate formation are validated by the Ti-O-C and N-O bonds using XPS and FTIR spectra. The photocatalytic activity of as-prepared photocatalyst was tested for the tetracycline degradation (TC, 10 mg/mL) under light irradiation. Significantly, 3 wt% carbon-doped TiO₂ (31CT) with Cu (II) hydroxide nitrate nanocomposite photocatalyst exhibited an excellent photocatalytic activity (97%, within 1 h), and the corresponding reaction rate was around 2 times higher than bare TiO₂. The excellent photocatalytic activity of 31CT-Cu nanocomposite was due to enhanced adsorbent of TC via carbon doping, visible light absorption, improved photo-generated carrier separation and migration by metal nitrate hydroxide as a support. This work may promote the development of a new carbon-doped TiO₂ supported with highly stable metal nitrate hydroxide nanocomposite by facile method and used as an efficient photocatalyst for photodegradation of environmental pollutants.

Al@TiO2 Core-Shell Nanoparticles for Plasmonic Photocatalysis

Plasmon-induced photocatalysis is a topic of rapidly increasing interest, due to its potential for substantially lowering reaction barriers and temperatures and for increasing the selectivity of chemical reactions. Of particular interest for plasmonic photocatalysis are antenna-reactor nanoparticles and nanostructures, which combine the strong light-coupling of plasmonic nanostructures with reactors that enhance chemical specificity. Here, we introduce Al@TiO₂ core-shell nanoparticles, combining earth-abundant Al nanocrystalline cores with TiO₂ layers of tunable thickness. We show that these nanoparticles are active photocatalysts for the hot electron-mediated H₂ dissociation reaction as well as for hot hole-mediated methanol dehydration. The wavelength dependence of the reaction rates suggests that the photocatalytic mechanism is plasmonic hot carrier generation with subsequent transfer of the hot carriers into the TiO₂ layer. The Al@TiO₂ antenna-reactor provides an earth-abundant solution for the future design of visible-light-driven plasmonic photocatalysts.

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...

Recent progress in transition metal oxide/sulfide quantum dots-based nanocomposites for the removal of toxic organic pollutants

Water is an essential solvent that is extremely necessary for the survival of life. Water pollution due to the increased utilization of water for various processes, including domestic and industrial activities, poses a special threat that contaminates both surface and ground water. In recent years, advanced oxidation processes (AOPs) have been applied to deal with wastewater problems, which is a green method used to oxidize organic contaminants with strong oxidative radical species. Among the AOPs, photocatalytic technology is one of the most promising strategies for wastewater cleaning, which fulfills the aims of environmentally friendly and sustainable development. Owing to their unique electronic, optical, and structural properties, nanoscale semiconductors have received substantial interest as materials for AOPs, particularly inspired by their superb quantum confinement effects and large surface-area-to-volume ratio, which are essential for catalytic reaction kinetics. Recent advancements have revealed that semiconductor nanocrystals, known as quantum dots (QDs), are newly emerging zero-dimensional (0-D) nanomaterials, which have garnered much attention owing to their special physiochemical characteristics such as high conductivity, thermo-chemical and opto-mechanical stability, high adsorption coefficients, and, most importantly, their admirable recyclability. In this review, we provide a clear understanding of the importance of semiconductor QD-based nanocomposites in the degradation of organic pollutants, in addition to the mechanism involved in the reaction process. Following this, the enhancement of different materials, such as metal oxides and metal sulfide QD-based nanocomposites, is discussed in the context of combating environmental pollution.

Synthesis, characterization and utilization of oxygen vacancy contained metal oxide semiconductors for energy and environmental catalysis

Developing novel functional materials with promising desired properties in enhancing energy conversion and lowering the catalytic reaction barriers is essential for the demand to solve the increasingly severe energy and environmental crisis nowadays. Metal oxide semiconductors (MOS) are widely used in the field of catalysis because of its excellent catalytic characteristics. Introduction of defects, in addition to the adjustment of composition and atomic arrangement in the materials can effectively improve the materials' catalytic performance. Especially, introducing oxygen vacancies (OVs) into the lattice structure of MOS has been developed as a facile route to improve MOS's optical and electronic transmission characteristics. And a large number of metal oxides with rich OVs have been served in oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO₂-RR) photo-degradation of organic pollutants, etc. This small review briefly outlines some preparation techniques to introduce OVs into MOS, and the characterization techniques to identify and quantify the OVs in MOS. The applications of OVs contained MOS especially in energy and environmental catalysis areas are also discussed. The effects of OVs types and concentrations on the catalytic performances are deliberated. Finally, the defective structure-catalytic property relationship is highlighted, and the future status and opportunities of MOS containing OVs in the catalytic field are suggested.

A carbon membrane-mediated CdSe and TiO2 nanofiber film for enhanced photoelectrochemical degradation of methylene blue

In this study, a carbon membrane-mediated CdSe and TiO₂ ternary film (CdSe/C/TiO₂) was prepared to degrade methylene blue (MB). Carbon membrane and CdSe were introduced to the surface of a TiO₂ nanofiber film via an in situ hydrothermal deposition process successively. The investigation shows that the carbon membrane not only provides a charge transfer channel to promote the transfer of electron from the conduction band of CdSe to that of TiO₂, but also improves the poor conduct between the TiO₂ film and electrolyte. The synergies between the carbon membrane and CdSe can make the ternary system harvest more visible light energy and facilitate the charge transfer property of TiO₂. The current density of CdSe/C/TiO₂ was about 9 folds higher compared with that of pure TiO₂ under UV and visible light irradiations. This ternary hybrid exhibits a superior activity during the photoelectrochemical (PEC) degradation of MB, and 92.43% can be removed after 120 min irradiation, which is improved by 21.14% than that of TiO₂.

A CdSe/C/TiO₂ nanofiber film was prepared for enhanced photoelectrochemical degradation ability, and carbon membrane as a carrier-transfer-channel could promote electron transfer.

Elucidating the Factors Affecting Hydrogen Production Activity Using a CdS/TiO2 Type-II Composite Photocatalyst

CdS/TiO2 is a composite photocatalyst that has been studied over many years and in which electron transfer from CdS to TiO2 is believed to lead to high photocatalytic activity. However, most reports on improved activity involve hydrogen production in the presence of a sulfide reducing agent. In this study, we comprehensively examined the effects of electron transfer, hydrogen overvoltage, substrate adsorption, and the cocatalyst from relationships between hydrogen production ability and the total number of trapped electrons in the presence of various reducing agents. As a result, we clarified that the electron transfer between CdS and TiO2 does not necessarily lead to high activity. We showed that the composite photocatalyst needs to be designed for the intended purpose and that evaluating the hydrogen production ability using sacrificial reagents provides insufficient information for use in an actual environment.

Highlights of the characterization techniques on inorganic, organic (COF) and hybrid (MOF) photocatalytic semiconductors

This review is dedicated to the brave COVID warriors fighting against the COVID-2019 pandemic.

Waste cigarette butt-derived nitrogen-doped porous carbon as a non-mercury catalyst for acetylene hydrochlorination

The development of advanced carbon materials as metal-free catalysts holds great importance for mercury catalyst replacement in acetylene hydrochlorination.

CdS quantum dots encapsulated within the mesopores of MCM-41 and interlayers of montmorillonite as photocatalysts for rhodamine-B degradation in aqueous solution

Capping agent-free CdS quantum dots (CdS-QDs) were synthesized within the mesopores of MCM-41 and interlayers of montmorillonite (MMT), using a safe manner by a facile ion exchange-precipitation protocol. The mesopores of MCM-41 and interlayers of MMT controlled the growth of CdS-QDs. The obtained CdS-QDs@MCM-41 and CdS-QDs/MMT were characterized by X-ray diffraction (XRD) analysis, energy-dispersive X-ray (EDX), diffuse reflectance UV-Vis, and photoluminescence spectroscopies. Photodegradation of rhodamine-B (RhB) over these embedded CdS-QDs was investigated under UV-Vis light irradiation. The influences of some parameters on the photodegradation of RhB such as pH, temperature, and UV-Vis irradiation time were investigated. The results showed that the CdS-QDs/MMT and CdS-QDs@MCM-41 have high efficiencies for RhB photodegradation under UV-Vis illumination.

Preparation of PVDF/CdS/Bi2WO6/ZnO hybrid membrane with enhanced visible-light photocatalytic activity for degrading nitrite in water

In this work, a visible light-driven ternary heterojunction photocatalyst, CdS/Bi₂WO₆/ZnO, was synthesized using hydrothermal, ultrasonic dispersion, and deposition precipitation methods. The results show that photocatalysts with flower-like heterostructures were obtained, which could efficiently separate electron-hole pairs, and the photocatalytic activity was thereby significantly enhanced. Furthermore, CdS/Bi₂WO₆/ZnO and polyvinylidene fluoride (PVDF) were used to fabricate hybrid membranes via a phase-conversion method. The samples were characterized using SEM, TEM, EDX, XRD, DRS, XPS, PL, and N₂ adsorption-desorption isotherms, and the transient photocurrent response. The photocatalytic activity of the hybrid membrane was evaluated, and 92.58% of the nitrite was converted into non-toxic substances within 4 h under simulated sunlight irradiation. This result indicated that the photocatalyst exhibited a good photocatalytic activity after immobilization. The possible mechanism was elucidated by studying the product during the photocatalytic degradation, and the effects of different pH values, electron scavengers, and hole scavengers on the photocatalytic performance were further investigated.

MOF-Derived Porous Fe2O3 Nanoparticles Coupled with CdS Quantum Dots for Degradation of Bisphenol A under Visible Light Irradiation

In this work, CdS quantum dots (QDs) were planted on magnetically recyclable porous Fe₂O₃ (denoted as F450) to obtain CdS QDs/porous Fe₂O₃ hybrids (denoted as X–CdS/F450, in which X is the immersion times of CdS QDs). Porous Fe₂O₃ was first obtained by pyrolysis from an iron-containing metal–organic framework by a two-step calcination method. Next, CdS QDs (of average size 3.0 nm) were uniformly and closely attached to the porous F450 via a sequential chemical-bath deposition strategy. As expected, the X–CdS/F450 hybrids serve as high-performance photocatalysts for the degradation of bisphenol A, a typical endocrine-disrupting chemical. Almost ∼100% of the bisphenol A was degraded over 5-CdS/F450 after visible light irradiation for 30 min (λ ≥ 420 nm). In comparison, the degradation efficiency of pure F450 powder is 59.2%. The high performance of 5-CdS/F450 may be ascribable to the fast electron transport of porous F450, the intense visible-light absorption of the CdS QDs and the matched energy levels between CdS and F450. More significantly, through the photocatalytic degradation reaction, the X–CdS/F450 hybrids can easily be recovered magnetically and reused in subsequent cycles, indicating their stability and recyclability.

Recent progress on the enhancement of photocatalytic properties of BiPO4 using π-conjugated materials

Semiconductor photocatalysis is regarded as most privileged solution for energy conversion and environmental application. Recently, photocatalysis methods using bismuth-based photocatalysts, such as BiPO₄, have been extensively investigated owing to their superior efficacy regarding organic pollutant degradation and their further mineralization into CO₂ and H₂O. It is well known that BiPO₄ monoclinic phase exhibited better photocatalytic performance compared to Degussa (Evonik) P25 TiO₂ in term of ultraviolet light driven organic pollutants degradation. However, its wide band gap, poor adsorptive performance and large size make BiPO₄ less active under visible light irradiation. However, extensive research works have been conducted in the past with the aim of improving visible light driven BiPO₄ activity by constructing a series of heterostructures, mainly coupled with π-conjugated architecture (e.g., conductive polymer, dye sensitization and carbonaceous materials). However, a critical review of modified BiPO₄ systems using π-conjugated materials has not been published to date. Therefore, this current review article was designed with the aim of presenting a brief current state-of-the-art towards synthesis methods of BiPO₄ in the first section, with an especial focuses onto its crystal-microstructure, optical and photocatalytic properties. Moreover, the most relevant strategies that have been employed to improve its photocatalytic activities are then addressed as the main part of this review. Finally, the last section presents ongoing challenges and perspectives for modified BiPO₄ systems using π-conjugated materials.

Superhigh flexibility and out-of-plane piezoelectricity together with strong anharmonic phonon scattering induced extremely low lattice thermal conductivity in hexagonal buckled CdX (XS, Se) monolayers

Although CdX (X = S, Se) has been mostly studied in the field of photocatalysis, photovoltaics, their intrinsic properties, such as, mechanical, piezoelectric, electron and phonon transport properties have been completely overlooked in buckled CdX monolayers. Ultra-low lattice thermal conductivity [1.08 W m-1K-1(0.75 W m-1K-1)] and high p-type Seebeck coefficient [1300μV K-1(850μV K-1)] in CdS (CdSe) monolayers have been found in this work based on first-principles DFT coupled to semi-classical Boltzmann transport equations, combining both the electronic and phononic transport. The dimensionless thermoelectric figure of merit is calculated to be 0.78 (0.5) in CdS (CdSe) monolayers at room temperature, which is comparable to that of two-dimensional (2D) tellurene (0.8), arsenene and antimonene (0.8), indicating its great potential for applications in 2D thermoelectrics. Such a low lattice thermal conductivity arise from the participation of both acoustic [91.98% (89.22%)] and optical modes [8.02% (10.78%)] together with low Debye temperature [254 K (187 K)], low group velocity [4 km s-1(3 km s-1)] in CdS (CdSe) monolayers, high anharmonicity and short phonon lifetime. Substantial cohesive energy (∼4-5 eV), dynamical and mechanical stability of the monolayers substantiate the feasibility in synthesizing the single layers in experiments. The inversion symmetry broken along thezdirection causes out-of-plane piezoelectricity. |d33| ∼ 21.6 pm V-1, calculated in CdS monolayer is found to be the highest amongst structures having atomic-layer thickness. Superlow Young's modulus ∼41 N m-1(31 N m-1) in CdS (CdSe) monolayers, which is comparable to that of planar CdS (29 N m-1) and TcTe2(34 N m-1), is an indicator of its superhigh flexibility. Direct semiconducting band gap, high carrier mobility (∼500 cm2V-1s-1) and superhigh flexibility in CdX monolayers signify its gigantic potential for applications in ultrathin, stretchable and flexible nanoelectronics. The all-round properties can be synergistically combined together in futuristic applications in nano-piezotronics as well.

Gas-Phase Photoelectrocatalytic Oxidation of NO via TiO2 Nanorod Array/FTO Photoanodes

Most photoelectrocatalytic (PEC) reactions are performed in the liquid phase for convenient electron transfer in an electrolyte solution. Herein, a novel PEC reactor involving a tandem combination of TiO₂ nanorod array/fluorine-doped tin oxide (TiO₂-NR/FTO) working electrodes and an electrochemical auxiliary cell was constructed to drive the highly efficient PEC oxidation of indoor gas (NO_x). With the aid of a low bias voltage (0.3 V), the as-formed PEC reactor exhibited an 80% removal rate for oxidizing NO (500 ppb) under light irradiation, which is much higher than that of the traditional photocatalytic (PC) process. Upon being irradiated by light, the photogenerated electrons are quickly separated from the holes and transferred to the counter electrode (Pt) owing to the applied bias voltage, leaving photogenerated holes in the TiO₂-NR/FTO electrode for oxidizing NO molecules. Moreover, both dry and humid NO could be effectively removed by the tandem TiO₂-NR/FTO-based gas-phase PEC reactor, indicating that the NO molecules could also be directly oxidized by photogenerated holes in addition to hydroxyl radicals. The presence of trace amounts of water could promote the PEC oxidation of NO owing to the formation of hydroxyl radicals induced by reactions between the water and holes, which could further oxidize NO. This PEC reactor offers an energy-saving, environmentally friendly, and efficient route to treat air polluted with low concentrations of gases (NO_x and SO_x).

A direct Z-scheme Bi2WO6/NH2-UiO-66 nanocomposite as an efficient visible-light-driven photocatalyst for NO removal

To explore an efficient photocatalyst for NO pollution, a direct Z-scheme photocatalytic system is successfully fabricated by coupling Bi₂WO₆ with NH₂-UiO-66 via a simple hydrothermal synthesis technique. The Z-scheme system promotes the NO photocatalytic oxidation activity with an optimum NO removal rate of 79%, which is 2.7 and 1.2 times that obtained by using only pristine Bi₂WO₆ and NH₂-UiO-66, respectively. Simultaneously, superior selectivity for converting NO to NO₃⁻/NO₂⁻ is observed. The enhanced photocatalytic performance of the Bi₂WO₆/NH₂-UiO-66 hybrids is attributed to the following two aspects: (i) large specific area of NH₂-UiO-66, which exposes more active sites and is beneficial to the adsorption and activation of NO; (ii) outstanding Z-scheme structure constructed between BiWO₆ and NH₂-UiO-66, which can improve the efficiency of the separation of electron–hole pairs and preserves the strong oxidation ability of hybrids. ESR analysis shows that ·O₂⁻ and ·OH contribute to NO removal. A possible photocatalytic mechanism of NO oxidation on the direct Z-scheme photocatalyst (BWO/2NU) under visible light irradiation is proposed. This work displays the BWO/2NU hybrid's potential for treating low-concentration air pollutants, and the proposed Z-scheme photocatalyst design and promotion mechanism may inspire more rational synthesis of highly efficient photocatalysts for NO removal.

To explore an efficient photocatalyst for NO pollution, a direct Z-scheme photocatalytic system is successfully fabricated by coupling Bi₂WO₆ with NH₂-UiO-66 via a simple hydrothermal synthesis technique.

Facile Fabrication of C-TiO2 Nanocomposites with Enhanced Photocatalytic Activity for Degradation of Tetracycline

Visible-lightdriven C-TiO₂ nanocomposites were prepared via a simple calcination and acid etching process. The C-TiO₂ nanocomposites were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, X-ray diffraction, transmission electron microscopy, and high-resolution TEM. The results showed that TiO₂ nanoparticles were combined with a porous carbon layer through surface C-O groups, which facilitates the strong interface interaction. The interface combination of nano-TiO₂ and carbon material increases the specific surface area of nano-TiO₂, widens the range of light response, and improves the efficiency of light-induced electron migration. The visible-light photocatalytic activity of the prepared photocatalyst was evaluated by the decomposition of tetracycline aqueous solution. Compared with that of pure TiO₂, the photocatalytic activity of C-TiO₂ nanocomposites was significantly improved. Furthermore, a possible photocatalytic mechanism was also tentatively proposed. This work can promote the development of active photocatalysts under solar light for the photodegradation of environmental pollutants.

A highly luminescent quantum dot/mesoporous TiO2 nanocomplex film under controlled energy transfer

We have prepared a highly luminescent quantum dot (QDs)-TiO2 nanocomplex film by the dip coating method. Because QDs with 3-mercaptopropionic acid as a ligand adsorb ionized Ti+ cations on the TiO2 particle, the average distance between the QDs can be changed through controlling the porosity in the film. The porosity is controlled using ethyl cellulose (EC). EC is the best material for well dispersing the hydroxyl functional group (-OH) in the chemical structure, and forming pores inside the film under the decomposition temperature (above 698 °F). As the porosity decreases, the average decay time controlled by the porosity increases to the maximum 91.2 ns. On the other hand, the amount of QDs decreased to 50%, hindering the increase of photo-luminescence (PL) intensity. Through this result, we have found that the PL intensity of the QD films is strongly related to the amount of the QDs and the resolution of aggregation. Consequently, we have optimized the porosity of the film and obtained high PL intensities up to approximately 17 times.

Size-Dependent Photocatalytic Activity of Carbon Dots with Surface-State Determined Photoluminescence

Carbon dots (CDs) were synthesized by a microwave-mediated method and separated by size exclusion chromatography into three different size fractions. There was no correlation of the size with photoluminescence (PL) emission wavelength, which shows that the PL mechanism is not quantum-size dependent. UV/vis absorption and diffuse reflectance spectroscopies showed that the light absorption properties as well as the band gap of the CDs changed with the size of the particle. The combination of FTIR and XPS measurements revealed the composition on the surface of each fraction. The three CDs fractions were separately used in the photocatalytic degradation of organic dyes under simulated sunlight irradiation. The catalytic activity of the as-prepared CDs was found to increase as the size of the particles decreased. Complete degradation of both rhodamine B (RhB) and methylene blue (MB) was achieved in 150 min by the 2-nm CDs. The scavenger studies showed that the holes and superoxide radicals are the main species involved in the photocatalytic degradation of the dye by the 2-nm CDs. These CDs displayed high stability in the degradation of organic dyes for multiple cycles. The 2-nm CDs displayed promising photocatalytic degradation of p-nitrophenol (PNP) . These results demonstrate for the first time the application of bare carbon dots in the degradation of environmental contaminants.

Electrophoretic deposition of photocatalytic materials

Powdered photocatalytic materials have been successfully applied for the degradation of organic and inorganic pollutants as well as for hydrogen production and CO₂ photo-reduction. However, the development of strategies for the preparation of photoactive coatings is a hot topic since it is a promising step for its use in photocatalytic reactors on an industrial scale. Electrophoretic deposition is a versatile technique capable to produce coatings of nanoparticles at a relative low cost and with an excellent quality and control of the deposited material. This work summarizes the fundamental aspects of the electrophoretic deposition process, as well as the latest contributions in the deposition of several photocatalytic materials including TiO₂ and other UV-photocatalysts like ZnO, ZnS, SrTiO₃ and PbMoO₄ in addition to visible-light-driven photocatalysts such as Bi₂O₃, CdS, CdSe, g-C₃N₄, among others. Furthermore, the morphological features of the coatings along with the repercussion in the photocatalytic performance are issues discussed in the present review, based on the effect of the multiple parameters of the electrophoretic process such as the applied voltage, the deposition time, the inter-electrode distance, the concentration of the particles, the solvents and additives.

Enhanced Photocatalytic Degradation of Organic Dyes via Defect-Rich TiO2 Prepared by Dielectric Barrier Discharge Plasma

The dye wastewater produced in the printing and dyeing industry causes serious harm to the natural environment. TiO₂ usually shows photocatalytic degradation of dye under the irradiation ultravilet light rather than visible light. In this work, a large number of oxygen vacancies and Ti³⁺ defects were generated on the surface of the TiO₂ nanoparticles via Ar plasma. Compared with pristine TiO₂ nanoparticles, the as-obtained Ar plasma-treated TiO₂ (Ar-TiO₂) nanoparticles make the energy band gap reduce from 3.21 eV to 3.17 eV and exhibit enhanced photocatalytic degradation of organic dyes. The Ar-TiO₂ obtained exhibited excellent degradation properties of methyl orange (MO); the degradation rate under sunlight irradiation was 99.6% in 30 min, and the photocatalytic performance was about twice that of the original TiO₂ nanoparticles (49%). The degradation rate under visible light (λ > 400 nm) irradiation was 89% in 150 min, and the photocatalytic performance of the Ar-TiO₂ was approaching ~4 times higher than that of the original TiO₂ nanoparticles (23%). Ar-TiO₂ also showed good degradation performance in degrading rhodamine B (Rho B) and methylene blue (MB). We believe that this plasma strategy provides a new method for improving the photocatalytic activity of other metal oxides.

Paper based modification-free photoelectrochemical sensing platform with single-crystalline aloe like TiO2 as electron transporting material for cTnI detection

By controlling target-induced signal quencher release, a label-free and modification-free microfluidic paper based photoelectrochemical analytical device (μ-PAD) for cardiac troponin-I (cTnI) detection was designed for the first time. To achieve it, cellulose paper based single-crystalline three-dimensional aloe like TiO₂ arrays (PSATs) were firstly fabricated as the electron transporting material, providing direct pathways for the charge carriers transfer, and subsequently coupled with CdS to form PSATs/CdS heterojunction for extending the solar spectrum response. Meanwhile, positive charged mesoporous silica nanoparticles (PMSNs) were prepared as the nanocarrier to efficient entrap the Cu²⁺ which could be regarded as signal quencher due to their reaction with CdS to form Cu_xS. Single stranded DNAs (ssDNAs), which could bind specifically with the target of cTnI, were then introduced to couple with the PMSNs and used as the bio-gate to encapsulate the signal quencher of Cu²⁺, endowing the functional PMSNs with responsiveness to cTnI. When the cTnI existed, the ssDNAs were dissociated from PMSNs due to the formation of cTnI-ssDNAs complexes, triggering controllable release of the trapped Cu²⁺, and further decreasing the photocurrent signal caused by the formation of Cu_xS. Accordingly, the concentration of cTnI could be accurately quantified via the photocurrent, realizing the target-induced modification-free μ-PAD assay. We believe this work could provide an ingenious idea to construct the easy-to-use novel modification-free μ-PAD.

Recent Progress on Titanium Dioxide Nanomaterials for Photocatalytic Applications

Environmental and energy problems have drawn much attention owing to rapid population growth and accelerated economic development. For instance, photocatalysis, "a green technology", plays an important role in solar-energy conversion owing to its potential to solve energy and environmental problems. Recently, many efforts have been devoted to improving visible-light photocatalytic activity by using titanium dioxide as a photocatalyst as a result of its wide range of applications in the energy and environment fields. However, fast charge recombination and an absorption edge in the UV range limit the photocatalytic efficiency of TiO₂ under visible-light irradiation. Many investigations have been undertaken to overcome the limitations of TiO₂ and, therefore, to enhance its photocatalytic activity under visible light. The present literature review focuses on different strategies used to promote the separation efficiency of electron-hole pairs and to shift the absorption edge of TiO₂ to the visible region. Current synthesis techniques used to elaborate several nanostructures of TiO₂ -based materials, recent progress in enhancing visible photocatalytic activity, and different photocatalysis applications will be discussed. On the basis of the studies reported in the literature, we believe that this review will help in the development of new strategies to improve the visible-light photocatalytic performance of TiO₂ -based materials further.

Studies on mass production and highly solar light photocatalytic properties of gray hydrogenated-TiO2 sphere photocatalysts

In this paper, it is first reported that gray hydrogenated TiO₂ sphere photocatalysts (H-TiO₂) with high reactivity to solar light are mass produced within a few minutes using an underwater discharge plasma modified sol-gel method at room temperature and atmospheric pressure. This plasma modified system is an easy one-step in-situ synthetic process and the crystallinity, hydrogenation, and spherical structure of H-TiO₂ are achieved by the synergy effect between the continuous reaction of highly energetic atomic and molecular species generated from the underwater plasma and surface tension of water. The resultant H-TiO₂ demonstrated high anatase/rutile bicrystallinity and extended optical absorption spectrum from the ultraviolet (UV) to visible range. Furthermore, various defects including oxygen vacancies and hydroxyl species on the TiO₂ surface permitted the enhancement of the photocatalytic performance. It was demonstrated that H-TiO₂ photocatalysts showed significant degradation efficiencies for reactive black 5 (RB 5), rhodamine B (Rho B), and phenol (Ph) under solar light irradiation, up to approximately 5 times higher than that of commercial anatase TiO₂ (C-TiO₂), which resulted in good water purification. Notably, it was also possible to cultivate HepG2 cells using such well-purified water (to degrees up to 76%), with minimal cytotoxicity. Considering all these results, we believe that this novel plasma technology is promising for important environmental applications.

TiOxNy Modified TiO2 Powders Prepared by Plasma Enhanced Atomic Layer Deposition for Highly Visible Light Photocatalysis

In this work, TiN film deposited by plasma enhanced atomic layer deposition (PEALD) is adopted to modify the commercial anatase TiO₂ powders. A series of analyses indicate that the surface modification of 20, 50 and 100 cycles of TiN by PEALD does not change the morphology, crystal size, lattice parameters, and surface area of TiO₂ nano powders, but forms an ultrathin amorphous layer of nitrogen doped TiO₂ (TiO_xN_y) on the powder surfaces. This ultrathin TiO_xN_y can facilitate the absorption of TiO₂ in visible light spectrum. As a result, TiO_xN_y coated TiO₂ powders exhibit excellent photocatalytic degradation towards methyl orange under the visible light with good photocatalytic stability compared to pristine TiO₂ powders. TiO_xN_y (100 cycles PEALD TiN) coated TiO₂ powders exhibit the excellent photocatalytic activity with the degradation efficiency of 96.5% in 2 hours, much higher than that of pristine TiO₂ powder of only 4.4%. These results clearly demonstrate that only an ultrathin surface modification layer can dramatically improve the visible light photocatalytic activity of commercial TiO₂ powders. Therefore, this surface modification using ALD is an extremely promising route to prepare visible light active photocatalysts.