Visible Light-induced Photocatalytic Activity Research Articles

Zn-Doped MnCO3/CS Composite Photocatalyst for Visible-Light-Driven Decomposition of Organic Pollutants.

Zn-doped MnCO3/carbon sphere (Zn-doped MnCO3/CS) composites were synthesized using a simple hydrothermal procedure. Among various samples (ZM-50, ZM-05, and ZMC-0), the ternary Zn-doped MnCO3/CS (ZMC-2) catalyst demonstrated excellent visible light-induced photocatalytic activity. This improvement comes from the Zn addition and the conductive CS, which facilitate electron movement and charge transport. The catalyst exhibited efficient degradation of methylene blue (MB) over a wide pH range, achieving a removal efficiency of 99.6% under visible light. Radical trapping experiments suggested that •OH and •O2- played essential roles in the mechanism of organic pollutant degradation. Moreover, the catalyst maintained good degradation performance after five cycles. This study offers valuable perspectives into the fabrication of carbon-based composites with promising photocatalytic activity.

Plasmonic Photocatalysts Based on Au Nanoparticles and WO3 for Visible Light-Induced Photocatalytic Activity

In this work, we report the application of Au/WO3 composite as a photocatalyst for the degradation of dyes under solar light irradiation. Au/WO3 nanocomposites were synthesized using an acid precipitation method followed by an impregnation/reduction at room temperature. Two composites were obtained by loading gold nanoparticles on two morphologies of nanostructured WO3, nanoplatelets (NP), and pseudospheres (PS). The elaboration parameters of the nanocomposites were optimized according to the gold mass percentage, the HAuCl4 precursor concentration, and the impregnation time. The structural, microstructural, and textural characterization were conducted using advanced techniques: XRD, SEM/TEM microscopies, and XPS and DRS spectroscopies. The optimal synthesis parameters are a 48 h impregnation of a five mass percentage of gold from a HAuCl4 precursor with a concentration of 10−3 mol·L−1. The obtained composites were formed with Au nanoparticles of 7 nm in size. The XRD analyses did not reveal any modification of the oxide supports structure after gold grafting, contrary to the sorption analyses, which evidenced a change in the state of the materials surface. XPS analysis revealed the reduction of W6+ ions into W5+, favoring the presence of oxygen vacancies. Furthermore, a localized surface plasmon resonance effect was observed in the composite at 540 nm. The photocatalysis results of several dye pollutants have shown a selective degradation efficiency depending on the charge of the polluting molecules, pH medium, and mass loading of the catalysts. At the native pH, the photocatalysis process is highly efficient on a cationic molecule, with a low adsorption capacity. Au/WO3 PS composite appears to be the most efficient, degrading almost the whole RhB and MB only in 60 min and 90 min, respectively, while, for the MO anionic dye, the degradation is more efficient in acidic medium (80%) than in basic medium (0%). Trap tests of the main active species were investigated and a photodecomposition mechanism is proposed.

Natural Diatomite Supported Zirconium-Doped TiO2 with Tailoring Band Structure for Enhanced Visible-Light Photocatalytic Properties.

The development of economically applicable, highly efficient and low cost photocatalytic materials has always been a challenge. In this work, we report a zirconium doped TiO/diatomite (ZrTD) composite with enhanced visible light-induced photocatalytic activity. The as-prepared samples were characterized by X-ray diffraction, scanning electron microscopy, UV–VIS diffused reflectance spectroscopy, high-performance liquid chromatography-mass spectrometry, photoluminescence and X-ray photoelectron spectroscopy, respectively. The optimal doping ratio of zirconium into TiO was obtained at 3% (3%ZrTD composite), and the degradation rate constant of which tetracycline (TC) is up to around 8.65 times higher that of zirconium doped TiO. In addition, zirconium doping introduces the impurity levels of Zr 3d and oxygen vacancies into the lattice of TiO, resulting in broadening the light absorption range, reducing the band gap, and improving the separation efficiency of photogenerated electron-hole pairs, thus endowing with visible light photocatalytic properties. Moreover, both the photogenerated holes (h) and superoxide (•O) radicals are responsible for the degradation process of TC, and a possible degradation pathway and the corresponding intermediate products of TC by ZrTD composite are also proposed in detail.

Mesoporous Nano-Sized BiFeVOx.y Phases for Removal of Organic Dyes from Wastewaters by Visible Light Photocatalytic Degradation.

With an increasing demand for industrial dyes in our daily lives, water conditions have become worse. Recently, the removal of such environmentally hazardous pollutants from wastewaters through photocatalytic degradation has been drawing increased attention. Three mesoporous nanophases of BiFeVOx.y as (Bi2FeIIIV1−yO5.5−y) visible light photocatalysts were synthesized in this study using ethylene glycol-citrate sol-gel synthesis combined with microwave- assisted calcination. X-ray diffraction (XRD), differential thermal analysis (DTA), FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM-EDS), nitrogen adsorption-desorption isotherms, and UV-Vis diffuse reflectance spectrophotometry (UV-Vis/DRS) were used to characterize the BiFeVOx.y photocatalysts. The visible light-induced photocatalytic activities of the BiFeVOx.y phases were evaluated by the degradation of methylene blue (MB) dye in aqueous solution at pH ~10.0. The results of this study show that the combination of doping strategy with the utilization of advanced synthesis methods plays an important role in improving the structure and surface properties of BiFeVOx.y phases, and thereby enhancing their adsorption and photocatalytic efficiencies. The synthesized mesoporous tetragonal γ-BiFeVOx.y nanophase has been proven to be a potential visible-light photocatalyst for the degradation of organic dyes.

Graphitic Carbon Nitride as a New Sustainable Photocatalyst for Textile Functionalization.

As a promising organic semiconducting material, polymeric graphitic carbon nitride (g-C3N4) has attracted much attention due to its excellent optical and photoelectrochemical properties, thermal stability, chemical inertness, nontoxicity, abundance, and low cost. Its advantageous visible light-induced photocatalytic activity has already been beneficially used in the fields of environmental remediation, biological applications, healthcare, energy conversion and storage, and fuel production. Despite the recognized potential of g-C3N4, there is still a knowledge gap in the application of g-C3N4 in the field of textiles, with no published reviews on the g-C3N4-functionalization of textile materials. Therefore, this review article aims to provide a critical overview of recent advances in the surface and bulk modification of textile fibres by g-C3N4 and its composites to tailor photocatalytic self-cleaning, antibacterial, and flame retardant properties as well as to create a textile catalytic platform for water disinfection, the removal of various organic pollutants from water, and selective organic transformations. This paper highlights the possibilities of producing g-C3N4-functionalized textile substrates and suggests some future prospects for this research area.

Visible light-induced photocatalytic and antibacterial activity of TiO2/polyaniline-kapok fiber nanocomposite

Anatase TiO2 nanoparticles with an average crystallite size of around 6.06 nm were successfully immobilized on the surface of polyaniline-coated kapok fiber (PANI-KpF) via hydrothermal reaction. The photocatalytic activity of the TiO2/PANI-KpF nanocomposite was studied under visible light using methyl orange (MO) and Cr(VI) as model pollutants. Photodegradation of MO was achieved using nanocomposites prepared with 0.5 and 1.0 mL titanium isopropoxide (TTIP) with removal efficiencies of about 87.4 and 76.8%, respectively. These are about 13 and 18% higher than the removal efficiencies under dark conditions. On the other hand, visible light-induced photo-reduction of Cr(VI) was carried out in the presence of isopropanol (IPA) as a hole scavenger, with 100% removal efficiency. Without IPA, Cr(VI) was removed by adsorption. The TiO2/PANI-KpF also showed antibacterial activity against E. coli bacteria under visible light.

Cerium oxide (CeO2-x) nanoparticles with high Ce3+ proportion synthesized by pulsed plasma in liquid

Cerium oxide (CeO2-x) nanoparticles were synthesized using a simple one-step method known as the pulsed plasma in liquid (PPL). XRD analysis showed the production of pure cubic cerium oxide (Fm 3‾ m). HRTEM and XANES analysis confirmed the monophase cubic CeO2-x, and exclude the presence of the hexagonal Ce2O3 and/or mix phase of CeO2/Ce2O3 in the particle layers. HRTEM analysis showed that most particles were about 3 nm in diameter. XPS analysis showed that the cerium oxide nanoparticles synthesized by the PPL method had a higher Ce3+ proportion (42.2%) than some commercial powders, and also higher than the previous reported nanoparticles. The present cerium oxide nanoparticles showed high visible light-induced photocatalytic activity in the degradation of methyl orange (MO) and better polishing characteristics of quartz glass, compared to commercial samples. These results may attribute to the high Ce3+-ion content and/or the small particle size.

Defective TiO2 Core-Shell Magnetic Photocatalyst Modified with Plasmonic Nanoparticles for Visible Light-Induced Photocatalytic Activity

In the presented work, for the first time, the metal-modified defective titanium(IV) oxide nanoparticles with well-defined titanium vacancies, was successfully obtained. Introducing platinum and copper nanoparticles (NPs) as surface modifiers of defective d-TiO2 significantly increased the photocatalytic activity in both UV-Vis and Vis light ranges. Moreover, metal NPs deposition on the magnetic core allowed for the effective separation and reuse of the nanometer-sized photocatalyst from the suspension after the treatment process. The obtained Fe3O4@SiO2/d-TiO2-Pt/Cu photocatalysts were characterized by X-ray diffractometry (XRD) and specific surface area (BET) measurements, UV-Vis diffuse reflectance spectroscopy (DR-UV/Vis), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). Further, the mechanism of phenol degradation and the role of four oxidative species (h+, e−, •OH, and •O2−) in the studied photocatalytic process were investigated.

Impact of Tetrazolium Ionic Liquid Thermal Decomposition in Solvothermal Reaction on the Remarkable Photocatalytic Properties of TiO2 Particles.

Ionic liquids (ILs) could serve as a structuring agent, a solvent, or a source of dopant during solvothermal synthesis of semiconductors particles. To understand the role of IL during formation of TiO2 particles, it is necessary to study the stability of this IL in solvothermal synthesis conditions, as well as studying the surface properties of formed TiO2 particles. In view of this, the effect of the 2,3,5-triphenyltetrazolium chloride IL ([TPTZ][Cl]) thermal decomposition during the solvothermal reaction and IL content in the reaction system on photoactivity of TiO2 microparticles has been systematically investigated. The samples obtained by using [TPTZ][Cl] exhibited remarkable photocatalytic properties in phenol degradation reaction under visible light. HPLC analysis of the solvothermal reaction medium and X-ray photoelectron spectroscopy (XPS) analysis of TiO2 particles revealed that [TPTZ][Cl] was decomposed completely and was incorporated into the TiO2 lattice. Generally, increasing the reaction time (1, 4, 12, and 24 h) promoted the TiO2 microspheres formation, as well as raising the visible light-induced photocatalytic activity of the photocatalysts. Longer reaction time was also accompanied by an increase in the efficiency of 2,3,5-triphenyltetrazolium chloride decomposition. The properties of the photocatalysts were investigated by means of UV-VIS diffuse reflectance spectroscopy (DRS), BET surface area measurements, scanning electron microscopy (SEM), X-ray powder diffraction (XRD) analysis, and XPS.

Fewer-layer BN nanosheets-deposited on Bi2MoO6 microspheres with enhanced visible light-driven photocatalytic activity

Photocatalysis is a process to convert light energy into chemical energy. And photocatalysis has been widely implemented into various areas, such as energy storage and environmental remediation. In this work, we focused on photocatalytic oxidation of organic pollutants in water on a new composite, i.e. BN-Bi2MoO6. The result suggests BN nanosheets may be an excellent co-catalyst in boosting the photocatalytic activity of the substrate (Bi2MoO6) in the decomposition of organics in water under visible light. This work sheds a light on addressing the importance of two-dimensional materials to suppress the recombination of photogenerated charge carriers, therefore to improve the visible light-induced photocatalytic activity.

Effects of crystallinity, {001}/{101} ratio, and Au decoration on the photocatalytic activity of anatase TiO2 crystals

Anatase TiO2 nanocrystals and sub-microcrystals with truncated octahedral bipyramidal morphologies were prepared by direct calcination of TiOF2 precursors. The as-prepared TiO2 samples were thoroughly characterized by X-ray diffraction, Raman spectroscopy, field-emission scanning electron microscopy, N2 adsorption-desorption isotherms, X-ray photoelectron spectroscopy, and UV-visible diffuse spectroscopy. It was found that the crystallinity, grain size, and {001}/{101} ratio of the samples can be increased by raising the calcination temperature from 500 to 800 °C. The higher crystallinity and {001}/{101} facet ratio resulted in an increase in both aqueous and gas-phase photocatalytic activities, by inhibiting the recombination and separation of electrons and holes. After selecting two TiO2 samples with high crystallinity and {001}/{101} ratio, Au nanoparticles were decorated on their surfaces, and the photocatalytic activity of the resulting samples under visible light illumination was studied. It was found that the visible light-induced photocatalytic activity increased by 2.6 and 4.8 times, respectively, upon Au decoration of the samples prepared by calcination of TiOF2 at 700 and 800 °C.

The sonochemical functionalization of MoS2 by zinc phthalocyanine and its visible light-induced photocatalytic activity

Here, the synthesis of a molybdenum disulfide–zinc phthalocyanine (MoS2–ZnTTBPc) composite is reported where the scalable synthesis of MoS2 was done by a simple solvothermal route followed by the sonochemical attachment of ZnTTBPc.

A new insight into the enhanced visible light-induced photocatalytic activity of NaNbO3/Bi2WO6 type-II heterostructure photocatalysts

In this study, a series novel NaNbO3/Bi2WO6 heterojunction composites with a type-II alignment were fabricated via a facile wet impregnation method. The as-prepared photocatalysts were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), diffuse reflectance UV-Vis spectroscopy (DRS), photocurrent (PC) and electrochemical impedance spectroscopy (EIS) analyses. The 30 wt% NaNbO3/Bi2WO6 composite exhibited the best performance in the case of degrading rhodamine B (RhB) aqueous solution under visible light irradiation (λ > 410 nm), which was ∼2.5 times and ∼40 times that of pure Bi2WO6 and NaNbO3, respectively. The improved photocatalytic performance was further demonstrated by 2-chlorophenol under the same reaction conditions. This may be attributed to the enhanced electron-hole separation efficiency in Bi2WO6 with the assistance of NaNbO3, as well as the dye-sensitization effect of RhB dye itself. Intermediates produced during the reaction and RhB degradation pathway were investigated as well. Radical quenching experiments revealed h+ played the predominant role; O2·- functioned as well to some degree. Based on experimental results, the potential functioning mechanism was proposed, which is different from previously reported type-II heterostructure systems when Bi2WO6 works as the electron reservoir and O2·- is one of the dominant active species. The as-prepared photocatalyst composite exhibited excellent stability after repetitively running five times. Effects of several operating parameters on the catalyst performance including initial RhB concentration, catalyst dosage, reaction temperature and initial pH were also discussed. This study provides solid evidence for NaNbO3 to be a promising candidate for photocatalysis and gives out a novel photocatalytic mechanism of Bi2WO6-based heterostructures.

Synthesis and enhanced visible light-induced photocatalytic activity of a hierarchical porous biomorphic N/Zn–TiO2@NH2-MIL-125 photocatalyst

Heterojunction is considered as very promising material for various applications in photocatalysis. Herein, an efficient heterojunction photocatalyst N/Zn–TiO2@NH2-MIL-125 was successfully synthesized for photo-degradation organic oxidation by biological-templated method. The electron–hole pairs can be separated in space more efficiently because of heterojunction structure. Systematical analyses of spectroscopy and microscopy measurements revealed that N/Zn–TiO2@NH2-MIL-125 heterojunction materials exhibited hierarchical porous structure with high surface area of 366.02 m2 g−1 and outstanding optical properties. Photocatalytic activity was investigated by degradating of rhodamine B (1000 µM) under visible-light irradiation. The N/Zn–TiO2@NH2-MIL-125 showed enhanced photocatalytic activity for RhB degradation, which is respectively about 1.81 and 1.97 times higher than that of the pristine N/Zn–TiO2 and NH2-MIL-125. Various advanced spectroscopic characterizations were applied including photoluminescence, Mott–Schottky curves and electrochemical impedance spectroscopy. A possible mechanism of enhanced photocatalytic oxidation activity for N/Zn–TiO2@NH2-MIL-125 composite under visible light irradiation was discussed.

Effect of Configuration on the Photocatalytic Activity of AgNPs-TiO2 System

This paper studies the effect of the configuration of silver nanoparticles (AgNPs)-TiO2 on the visible-light-driven photocatalytic activity (PA). Three configurations were fabricated by vacuum thermal deposition: configuration I, AgNPs deposited on the surface of TiO2 thin films; configuration II, AgNPs deposited on a glass and covered by TiO2 thin films; and configuration III, AgNPs deposited on the surface of TiO2 thin films and covered by TiO2. The PAs of the three configurations were studied and compared. Our study indicates that configuration II is the most cost-efficient one, while configuration III could obtain the highest visible light-induced PA. The maximum of PA could be achieved when the top layer of TiO2 is less than 2 nm. The mechanisms were discussed from three aspects, the influence of TiO2 thickness on the localized surface plasma resonance (LSPR) of AgNPs, the separation, and the transportation of hot carriers. By this study, the most effective way to make use of the PA of TiO2-AgNPs was scientifically searched out.

Palladium nanoparticles and rGO co-modified BiVO4 with greatly improved visible light-induced photocatalytic activity

A ternary composite, Pd-rGO-BiVO4, was fabricated with reduced graphene oxide (rGO) and palladium nanoparticles decorated on the surface of BiVO4. As-prepared samples were tested for the photocatalytic degradation of phenol under visible light irradiation. Enhancement was observed for the ternary structure, merits of which may be as follows: 1) rGO wrapped BiVO4 facilitated the photogenerated electrons transfer, 2) palladium nanoparticles served as electron acceptors, 3) palladium nanoparticles on the surface were capable of absorbing visible light photons. The uptake of photogenerated charge carriers would improve their separation and more oxidative species may be produced that can participate in the degradation of organics. Due to the SPR effect of palladium nanoparticles on the surface, the harvesting capacity of the photocatalyst to absorb visible light photons was increased, and thus its photocatalytic activity was improved. It should be noted that phenol was more easily adsorbed by rGO due to the π-π interaction between rGO and phenol, which also contributed to the enhancement in the photocatalytic activity. This work provides new evidence to confirm the advances of ternary structures applied in the photocatalytic removal of phenolic compounds in water under visible light irradiation.

Microbial fuel cell assisted band gap narrowed TiO2 for visible light-induced photocatalytic activities and power generation

This paper reports a simple, biogenic and green approach to obtain narrow band gap and visible light-active TiO2 nanoparticles. Commercial white TiO2 (w-TiO2) was treated in the cathode chamber of a Microbial Fuel Cell (MFC), which produced modified light gray TiO2 (g-TiO2) nanoparticles. The DRS, PL, XRD, EPR, HR-TEM, and XPS were performed to understand the band gap decline of g-TiO2. The optical study revealed a significant decrease in the band gap of the g-TiO2 (Eg = 2.80 eV) compared to the w-TiO2 (Eg = 3.10 eV). The XPS revealed variations in the surface states, composition, Ti4+ to Ti3+ ratio, and oxygen vacancies in the g-TiO2. The Ti3+ and oxygen vacancy-induced enhanced visible light photocatalytic activity of g-TiO2 was confirmed by degrading different model dyes. The enhanced photoelectrochemical response under visible light irradiation further supported the improved performance of the g-TiO2 owing to a decrease in the electron transfer resistance and an increase in charge transfer rate. During the TiO2 treatment process, electricity generation in MFC was also observed, which was ~0.3979 V corresponding to a power density of 70.39 mW/m2. This study confirms narrow band gap TiO2 can be easily obtained and used effectively as photocatalysts and photoelectrode material.

Effects of Pt-loading on Formation and Visible Light-Induced Photocatalytic Activity of Bismuth Titanate

Effects of Pt-loading on Formation and Visible Light-Induced Photocatalytic Activity of Bismuth Titanate

Preparation, characterization and the antimicrobial properties of metal ion-doped TiO2 nano-powders

TiO2 samples doped with lithium, sodium, magnesium, iron or cobalt were prepared by high-energy ball milling for different periods of time. The crystalline phase, chemical composition, crystalline size and photo-absorption were characterized by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS) and Ultraviolet visible diffuse reflectance spectroscopy (UV - Vis - DRS), Fourier transform infrared spectroscopy (FT - IR) and scanning electron microscopy (SEM). The antimicrobial properties of the modified TiO2 samples were evaluated with E. coli and S.aureus assays. The results of the XRD show that the TiOSO4, Ti3O5, Li2TiO3 and NaTi2O4 phases appear along with Li, Na and Mg doped TiO2. However, XPS spectra indicated that Ti exists as both Ti3+ and Ti4+ in Na-doped TiO2 samples. Ti3+, due to its narrow band gap, is highly active in promoting visible light-induced photocatalytic activity. SEM images showed that the crystalline size of TiO2 is reduced and has a common-round and hexagonal plate morphology after milling. The modified TiO2 samples had the best antimicrobial activities after 3h of milling. In particular, the antimicrobial rate of TiO2 5% doped with transition metals (Co, Fe) reached 100% against E. coli, but the antibacterial rate against S. aureus for Co and Fe dopants was 98.4% and 98.2%, respectively.

Enhanced visible light-induced photocatalytic activity of surface-modified BiOBr with Pd nanoparticles

Abstract Palladium nanoparticles well-dispersed on BiOBr surfaces were successfully prepared via a two-step process, namely hydrothermal synthesis of BiOBr followed by photodeposition of palladium. Surface-exposed palladium nanoparticles may improve the harvesting capacity of visible light photons via the surface plasmonic resonance effect to produce extra electrons. Palladium is an excellent electron acceptor, and therefore favours the separation of photogenerated electron/hole pairs. As a result, palladium significantly improves the photocatalytic activity of BiOBr in the removal of organic pollutants (phenol) under visible light irradiation. In addition to as-prepared samples which were comprehensively characterized, the mechanism for the enhancement via the deposition of palladium nanoparticles was also proposed based on results. This work may serve as solid evidence to confirm that surface-deposited palladium nanoparticles are capable of improving photocatalytic activity, and that photodeposition may be an effective approach to load metal nanoparticles onto a surface.