Remarkable Improvement Of Photocatalytic Activity Research Articles

Facile Synthesis of Oxygen-Doped g-C3N4 Mesoporous Nanosheets for Significant Enhancement of Photocatalytic Hydrogen Evolution Performance.

In this work, oxygen-doped g-C3N4 mesoporous nanosheets (O-CNS) were synthesized via a facile recrystallization method with the assistance of H2O2. The crystal phase, chemical composition, morphological structure, optical property, electronic structure and electrochemical property of the prepared O-CNS samples were well investigated. The morphological observation combined with the nitrogen adsorption-desorption results demonstrated that the prepared O-CNS samples possessed nanosheet-like morphology with a porous structure. Doping O into g-C3N4 resulted in the augmentation of the specific surface area, which could provide more active sites for photocatalytic reactions. Simultaneously, the visible light absorption capacity of O-CNS samples was boosted owing to the regulation of O doping. The built energy level induced by the O doping could accelerate the migration rate of photoinduced carriers, and the porous structure was most likely to speed up the release of hydrogen during the photocatalytic hydrogen process. Resultantly, the photocatalytic hydrogen production rate of the optimized oxygen-doped g-C3N4 nanosheets reached up to 2012.9 μmol·h-1·g-1, which was 13.4 times higher than that of bulk g-C3N4. Thus, the significantly improved photocatalytic behavior was imputed to the synergistic effect of the porous structure, the increase in active sites, and the enhancement of visible light absorption and charge separation efficiency. Our research highlights that the synergistic effect caused by element doping will make a great contribution to the remarkable improvement in photocatalytic activity, providing a new inspiration for the construction of novel catalysts.

Remarkable improvement in photocatalytic activity of g-C3N4 for NO oxidation through surface hydroxylation

The nitrogen oxide emissions originating from combustion pose significant risks to the environment. Photocatalysis is considered an efficient and environmentally friendly strategy to alleviate this problem. Graphitic carbon nitride (g-C3N4) is regarded as one of the most promising organic photocatalytic materials for environmental purification. However, its small specific surface area, weak adsorption and high recombination rate of charge carriers result in low intrinsic photocatalytic activity. To overcome these obstacles, a hydrothermal treatment of dicyandiamide-derived g-C3N4 (DCN) at different temperatures (140–200 °C) was employed to enhance the photocatalytic activity for NO oxidation. The experimental results demonstrated a significant improvement in the photocatalytic oxidation removal rate of NO after a hydrothermal treatment. The optimal photocatalyst, DCN-180, treated at 180 °C, demonstrated the highest NO removal efficiency (65.0 %), which is twice the value of pristine DCN (32.5 %). Additionally, the formation of the toxic intermediate NO2 was effectively suppressed during the reaction. Photoelectrochemical tests revealed that DCN-180 exhibited higher photocurrent density and smaller impedance radius compared to the untreated g-C3N4 sample. Moreover, density functional theory (DFT) calculations confirmed that the DCN-180 sample showed a stronger ability to adsorb O2 and NO. The enhanced photocatalytic NO oxidation performance of DCN-180 has been primarily attributed to its enlarged specific surface area (from 10.7 to 35.5 m2 g−1), local polarization effect, reduced interfacial charge transfer resistance, and improved adsorption abilities for NO and O2 molecules. This study provides valuable insights for designing and preparing highly efficient g-C3N4 based photocatalysts through surface modification for photocatalytic NO purification.

Remarkable improvement in photocatalytic activity of NiO nanoparticles through Ag doping: A kinetics-mechanism & recyclability

Metal oxides are recognized as exemplary materials for photocatalytic dye degradation attributed to their unique characteristics such as tunable electronic structure, prolonged stability, and cost-effectiveness. However, the wide band gap inherent to most of these materials often limits their light absorption to the ultraviolet (UV) region. Consequently, the doping of noble metal nanoparticles into the metal oxide nanostructures has been proposed to significantly improve their light-harvesting ability. This enhancement is primarily ascribed to the localized surface plasmon resonance (LSPR) effect associated with noble metal nanoparticles, which facilitates more effective utilization of light. Thus, in this study, we synthesized silver-doped nickel oxide (Ag:NiO) with varying Ag concentrations (0, 1, 2, 4, 6 wt%) to evaluate their photocatalytic performance. The X-ray diffraction (XRD) spectra revealed that NiO possesses a cubic crystalline structure, and a peak shift to a higher angle was noted for Ag doping, indicative of compressive strain. Further analyses of morphological, vibrational, and absorption properties were conducted through the acquisition of scanning electron microscopy (SEM) images, Raman spectra and UV–Vis absorption spectra, respectively. The photocatalytic degradation of methylene blue (MB) and rhodamine B (RhB) dyes was assessed, revealing that NiO with 4.wt.% Ag doping exhibited enhanced photocatalytic activity, achieving 99% degradation of MB and 90% degradation of RhB. Notably, Ag doping significantly enhances the light absorption capabilities and modifies the electronic structure of the NiO, thereby improving its performance in photocatalytic dye degradation.

Evaluation of photocatalytic activity, water contact angle, and annealing for TiO2 thin films deposited with mixed WOX–SiO2 thin films using radiofrequency sputtering

A mixture of hydrophilic silicon dioxide (SiO2) and visible-light-reactive tungsten oxide (WOX) has the potential to improve the photocatalytic activity of conventional titanium dioxide (TiO2). This study deposits mixed WOX–SiO2 thin films on TiO2 surfaces by controlling the composition of WOX:SiO2 using radiofrequency sputtering to improve photocatalytic activity and hydrophilicity. The photocatalytic activity is evaluated via the degradation of a methylene blue solution, and hydrophilicity is measured using the water contact angle. In addition, the effect of annealing is determined at 400 °C after deposition. The optical bandgap decreases as the composition of WOX increases and subsequently anneals. The XRD measurements show that polycrystalline monoclinic WO3 peaks appear after annealing when the composition of the mixed WOX–SiO2 thin films only consists of WOX. In contrast, monoclinic WO3 (200) appears after adding SiO2. Atomic force microscopy images show that the grain size decreases as the SiO2 content increases. Moreover, the photocatalytic activity of the mixed WOX–SiO2 thin films improves after annealing. In particular, the mixed WOX–SiO2 thin films that are deposited at a sputter power of WOX:SiO2 = 100:50 W demonstrate a remarkable improvement in photocatalytic activity. Furthermore, the water contact angle of the mixed WOX–SiO2 thin films decreases as the SiO2 content increases and after annealing. This proposed approach can be used for high-performance photocatalytic materials and be widely applied for the fabrication of various semiconducting devices.

Flexible TiO2 nanograss array film decorated with oxygen vacancies introduced by facile chemical reduction and their photocatalytic activity

Flexible TiO 2 nanograss array film was prepared by simple chemical oxidation of Ti wire mesh at a low temperature of 353 K. To improve its visible-light-driven photocatalytic activity, we further carried out a low-temperature chemical reduction to introduce oxygen vacancies in the solution of ethylene glycol (EG) and ammonium fluoride (NH4F). The results of XPS and EPR confirmed the formation of surface and bulk oxygen vacancies was confirmed, and their concentrations increased as the reduction time increased. Compared with the as-annealed TiO 2 film, the as-reduced specimens exhibited higher visible-light-driven photocatalytic activity. When reduction time was 48h, the photocatalytic activity was increased by 15.8 times compared to the as-annealed sample. The remarkable improvement in photocatalytic activity should be ascribed to the oxygen vacancies’ introduction. The most excellent photocatalytic performance was obtained when a suitable concentration ratio of surface oxygen vacancies to bulk oxygen vacancies was reached. Low-temperature chemical reduction in the solution of EG + NH4F is very efficient and convenient for introducing defects such as oxygen vacancies and Ti3+.

Synergetic Hybridization Effect of Homogeneously Mixed Inorganic and Graphene Nanosheets on the Photocatalytic Activity of Semiconductor

Using the homogeneous colloidal mixture of conductive metal oxide nanosheet (NS) and reduced graphene oxide (rGO) NS as hybridization matrices provides universal way of optimizing the photocatalyst functionality of semiconductor nanocrystals. A self‐assembly between CdS quantum dots (QDs) and RuO2/rGO NSs yields strongly coupled ternary nanohybrids with enhanced photocatalytic activity and increased porosity. Even with its lower RuO2 content, the ternary CdS−RuO2/rGO nanohybrid exhibits notably higher photocatalytic activities for visible‐light‐induced H2 evolution and photocurrent generation than binary CdS−RuO2/rGO homologues, underscoring the synergetic hybridization effect of flexible rGO and hydrophilic RuO2 NSs. In comparison with single RuO2/rGO NSs, their homogeneous mixture can play better roles of photosensitizers and cocatalysts, which is mainly responsible for remarkable improvement of photocatalytic activity upon the cohybridization with mixed RuO2/rGO NSs. The current study underscores that cohybridization with complementary inorganic and graphene NSs can provide an efficient and economically feasible methodology to explore novel high‐performance catalyst materials.

A remarkable improvement in photocatalytic activity of titanium dioxide nanoparticles through samarium doping synthesized by hydrothermal technique for water treatment

The aim of the present work is to investigate the influence of Samarium ions doping in the TiO2 host lattice and the contribution to the optical properties of this semiconductor. The X-ray diffraction pattern shows the formation of anatase phase TiO2 nanoparticles of average sizes 7.8 nm, 7.21 nm and 6.1 nm for both pure and 1 wt% and 4 wt% of Sm3+ doped samples respectivity. Energy Dispersive X-ray (EDX) spectroscopy confirms the presence of Sm ions within the Sm substituted TiO2 nanoparticles. These results suggest that, Pure and doped TiO2 samples confirm anatase phase of good crystallinity with smaller crystallite size. UV–visible spectra display stronger absorption in the visible region. The photocatalytic experiments are investigated by the removal of rhodamine B under UV light. Compared to the other two photocatalysts, the results shows that 4 wt% of Sm3+ doped TiO2 exposes the highest photocatalytic performance.

A remarkable improvement in photocatalytic activity of ZnO nanoparticles through Sr doping synthesized by one pot flash combustion technique for water treatments

Zinc oxide is well-known material and used in several applications. We have synthesized the good quality ZnO nanoparticles with different concentrations of Strontium (Sr) doping for photocatalytic applications. The elemental composition and homogeneous distribution of Sr doping in ZnO was investigated through EDX/SEM mapping. The morphology of synthesize products was studied through FE-SEM and grain size was estimated. X-ray diffraction (XRD) and FT-Raman spectroscopy analyses approves the single phase and purity of synthesized Sr:ZnO NPs as no additional peak in XRD and Raman was seen. The size of crystallites was estimated using Scherrer equation and noticed to be reduced from 24 to 16 nm with rising the Sr concentration. The energy gap was estimated using Kubelka-Munk function and noticed in range from 3.25–3.27 eV with Sr concentration. The photoluminescence spectra were recorded for all Sr:ZnO NPs at λexc =350 nm. The photocatalytic activity of Sr:ZnO NPs samples was investigation by decolourization of methylene blue (MB) dye under irradiation of black-light in an aqueous solution at ambient conditions. A remarkable improvement in photocatalytic activity was obtained for the entire prepared Sr:ZnO samples compared to that of neat ZnO. Such improvement in photocatalytic activity can be attributed to the effective photogenerated charges separating, in addition to the good adsorption of MB dye molecules over Sr:ZnO NPs surface.

Amorphous SiO2 nanofiber@CuO quantum dots with enhanced photocatalytic activity

Amorphous silicon dioxide (SiO2) fibers (ASF) loaded with well-dispersed copper (II) oxide (CuO) quantum dots were prepared through a hydrothermal process using copper hydroxide as the precursor. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen gas (N2) adsorption–desorption isotherm measurements and ultraviolet (UV)–visible spectroscopy. It was found that the surface of the fibers was decorated with well-dispersed copper (II) oxide quantum dots with 5 nm average size. The composites, with a high specific surface area of 78·52 m2/g, showed fierce light absorption within the UV band and low light absorption within the 400–600 nm and exhibited higher photocatalytic activities compared with pure copper (II) oxide for the photodegradation of potassium ethyl xanthate (KEX) under incandescent light. A decrease in agglomeration and an increase in the specific surface area of copper (II) oxide particles may have contributed to the results. The combination of copper (II) oxide quantum dots and ASFs can result in a remarkable improvement in photocatalytic activity and may provide a useful method for the degradation of KEX.

Enhancing photocatalytic H2 evolution from water on CuO-Co3O4/TiO2: The key roles of Co3O4 loading amounts

Spatially controlled co-loading of both oxidation and reduction cocatalysts on semiconductor photocatalysts has been demonstrated to be favorable for photogenerated charge separation and thus enhanced photocatalytic activity. Herein, we presented a simple ball-milling method to improve photocatalytic H2 production of TiO2 by co-loading of oxidation cocatalyst Co3O4 with reduction cocatalyst CuO, wherein the Co3O4 loading amount was significant especially for TiO2 loaded with sufficient or optimum CuO. In comparison with that on TiO2 loaded with only CuO, the photocatalytic H2 production from water over TiO2 photocatalyst co-loaded with CuO and trace Co3O4 was enhanced by approximately 5.5 times, even though complex spatial control was not adopted. In contrast, remarkable improvement of photocatalytic activity after Co3O4 co-loading was only observed on TiO2 photocatalysts loaded with less CuO in the presence of methanol. Better separation of photogenerated charges on the surface of dual-cocatalysts modified TiO2 was further demonstrated by decreased luminescence as well as increased photogenerated electrons and hydroxyl radicals as compared to those loaded with only CuO.

Synergic effect of Ag decoration onto ZnO nanoparticles for the remediation of synthetic dye wastewater

Highly efficient photocatalytic Ag-decorated ZnO nanopowders were fabricated via photodeposition method. The physical properties of synthesized nanopowders were rigorously investigated using analytical techniques, such as, powder XRD studies, HR-TEM and PL spectroscopy. The surface area of samples was obtained using BET analysis. The potential of synthesized nanopowders as photocatalyst was evaluated by studying the degradation of basonyl violet dye. Coating of ZnO nanopowders with metallic silver resulted in a remarkable improvement in photocatalytic activity. Moreover, most proficient conditions were deduced for the degradation of basonyl violet, by varying parameters, such as, catalyst loading, concentration of dye, and solution pH, using Ag-decorated ZnO nanopowders under UV irradiation.

Fabrication of morphology-controlled TiO2 photocatalyst nanoparticles and improvement of photocatalytic activities by modification of Fe compounds

Our previous studies suggested that redox reaction proceeded separately on specific exposed crystal faces of TiO2 nanoparticles. Site-selective deposition of metal or metal oxide on TiO2 specific exposed crystal faces successfully proceeded using the unique reactivity properties on the surface of TiO2 nanoparticles under photoexcitation. A remarkable improvement of photocatalytic activity of shape-controlled brookite and rutile TiO2 nanorods with modification of Fe3+ compounds was observed under visible light. Crystal face-selective metal compound modification on exposed crystal faces of TiO2 nanorods with brookite and rutile phases was successfully prepared. Brookite and rutile TiO2 nanorods prepared by site-selective modification with metal compounds should be ideal visible-light responsive TiO2 photocatalysts because of the remarkable suppression of back electron transfer from TiO2 to oxidized metal compounds on the surface of the TiO2 nanorod with a brookite or rutile phase. In this paper, the development of exposed crystal face-controlled TiO2 nanorods with rutile and brookite phases was described. The obtained rutile and brookite TiO2 nanorod, showing remarkably high activity for degradation of organic compounds compared with the photocatalytic activities of anatase fine particles (ST-01), is one of the most active commercially available photocatalysts for environmental cleanup in Japan. The technology of visible-light responsive treatment for morphology-controlled rutile and brookite TiO2 nanorods by crystal face-selective modification of Fe3+ compounds was also discussed in this paper. The Fe3+ compound-modified rutile and brookite TiO2 nanorods show much higher activity than conventional visible-light responsive N-doped TiO2, which is commercially available in Japan.

Preparation and enhanced photocatalytic activity of Pd–CuO/palygorskite nanocomposites

Silicate nanofibers (palygorskite, Pal) coated with CuO nanoparticles were prepared via a precipitation method using copper oxalate as a precursor and subsequently modified with PVP–Pd solution. Characterization by X-ray diffraction and transmission electron microscope demonstrated that the surfaces of the Pal fibers with 20–30nm in diameter and 400–500nm in length were uniformly decorated with CuO nanoparticles of 16nm in average size. The CuO/Pal and Pd–CuO/Pal nanocomposites exhibited higher photocatalytic activities than the pure CuO for the photodegradation of methyl orange under UV-light. The enhanced photocatalytic activity of CuO/Pal and Pd–CuO/Pal composites may be ascribed to the surface adsorption and efficient electron–hole separation at the coupled interface. The combination of nanoparticles and nano-scale fibers can lead to a remarkable improvement in photocatalytic activity; this concept can be expected to find interesting applications in the environmental field.

Enhanced photocatalytic activity of silica-embedded TiO2 hollow microspheres prepared by one-pot approach

Si-doped TiO2/carbon composite solid microspheres were prepared by a simple one-pot hydrothermal approach, using glucose, ammonium fluorotitaniate and ammonium fluorosilicate as raw materials. Then silica-embedded TiO2 hollow microspheres were obtained by calcination of the as-prepared precursor. Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), N2 adsorption–desorption measurement, X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectra (UV–vis DRS) were used to characterize the as-fabricated samples. Methylene blue (MB) solution was taken as the degradation model to evaluate the photocatalytic activity of the samples under ultraviolet light. The result showed that a remarkable improvement of photocatalytic activity for TiO2 hollow microspheres could be obtained by addition of silicon.

Heat treatment of nanometer anatase powder and its photocatalytic activity for degradation of acid red B dye under visible light irradiation

The phase transformation of nanometer TiO2 powder from anatase to rutile was realized by heat treatment, and a new nanometer TiO2 photocatalyst that could be excited by visible light was obtained. The heat-treated TiO2 powder at different transition stage was characterized by powder x-ray diffraction, transmission electron microscopy, and Fourier transform infrared spectroscopy. The test of photocatalytic activity of the heat-treated TiO2 powder was carried out by the photocatalytic degradation of acid red B dye in aqueous solution under visible light irradiation. The nanometer anatase TiO2 heat-treated at 500°C for 30 min exhibited much higher activity than those of pure anatase and mechanically mixed (anatase and rutile) TiO2. The remarkable improvement of photocatalytic activity was mainly illustrated by the special interphase between rutile and anatase, which not only restrains the recombination of photogenerated electron-hole pairs but also reduces the adsorbability of nanometer anatase TiO2 powder to a certain extent. More significantly, the anticipatory interlaced energy level of heat-treated TiO2 particles is convenient for capturing photons of low energy and thus achieves the intention of using visible light.

Solar photocatalytic degradation of dye wastewater in the presence of heat‐treated anatase TiO2 powder

AbstractThe phase transformation from anatase to rutile of titanium dioxide (TiO2) was attempted by heat‐treatment and a novel TiO2 catalyst with high photocatalytic activity under sunlight irradiation was obtained. The heat‐treated anatase TiO2 powders at various transition stages were characterized by X‐ray diffraction (XRD), fourier transform infrared (FTIR), and transmission electron microscopy (TEM). The tests of photocatalytic activities of the heat‐treated anatase TiO2 powders were conducted by the photocatalytic degradation of rhodamine B in aqueous solution under sunlight irradiation. The results reveal that the anatase TiO2 powder heat‐treated at 700°C for 60 min shows the highest photocatalytic activity, which can effectively degrade rhodamine B in aqueous solution under sunlight irradiation. The remarkable improvement of photocatalytic activity of the anatase TiO2 powders was mainly elucidated by the formation of special interphase between rutile and anatase phases, which can limit the recombination of photogenerated electrons and holes efficiently. Therefore, this method may be envisaged as a technology for treating dye wastewaters using solar energy. © 2008 American Institute of Chemical Engineers Environ Prog, 2008

Degradation of Hazardous Dyes in Wastewater using Nanometer Mixed Crystal TiO2 Powders under Visible Light Irradiation

The partial phase transformation of nanometer TiO2 powder from anatase phase to rutile phase was realized by heat-treatment and a new TiO2 photocatalyst which could be excited by visible light was obtained. The heat-treated TiO2 powder at different stage of transition crystal was characterized and monitored by XRD, TEM, FT-IR and UV–vis DRS methods. The test of photocatalytic activity of the heat-treated TiO2 powder was carried out by the photocatalytic degradation of rhodamine B and acid orange II dyes, respectively, in aqueous solution under visible light irradiation. The results indicate that the nanometer TiO2 photocatalyst heat-treated at 500°C for 60 min shows the highest photocatalytic activity, that is, it can effectively degrade the rhodamine B and acid orange II under visible light irradiation. The remarkable improvement of photocatalytic activity of heat-treated TiO2 powder at 500°C for 60 min was mainly illustrated by the formation of special interphase between rutile and anatase phases, which not only restrains the recombination of photogenerated electrons and holes, but also reduces the adsorbability of nanometer anatase TiO2 powder properly for various dyes. Additionally, the effects of dye-assisting chemicals such as Na2CO3 and NaCl on the photocatalytic degradation were also studied.

Photocatalytic degradation of dyestuff wastewater under visible light irradiation using micron‐sized mixed crystal TiO2 powders

AbstractA phase transformation of micron‐sized TiO2 powder from anatase to rutile was attempted by heat‐treatment in order to generate a new mixed crystal TiO2 with high associated photocatalytic activity. Heat‐treated micron‐sized TiO2 powders at different transition stages were characterized by X‐ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FT‐IR) and transmission electron microscopy (TEM) methods. The tests of photocatalytic activity of the heat‐treated micron‐sized TiO2 powders were conducted by the photocatalytic degradation of Rhodamine B and Acid Red B under visible light irradiation. The results indicate that mixed crystal TiO2 photocatalyst heat‐treated at 400 °C for 60 min shows the highest photocatalytic activity. It can effectively decompose the Rhodamine B and Acid Red B in aqueous solution after 6 h visible light irradiation. A remarkable improvement in photocatalytic activity of TiO2 is caused by the formation of combined rutile–anatase phases and separation of photogenerated electron–hole pairs. Copyright © 2007 Society of Chemical Industry

Investigation on degradation of azo fuchsine using visible light in the presence of heat-treated anatase TiO 2 powder

The phase transformation of TiO 2 powder from anatase phase to rutile phase was attempted by heat-treatment, and a new TiO 2 photocatalyst was obtained which could be excitated by visible light. The heat-treated TiO 2 powder at different transition stage was characterized by XRD, FT-IR and TEM methods. The test of photocatalytic activities of the heat-treated TiO 2 powders were carried out through the photocatalytic degradation of azo fuchsine dye in aqueous solution under the irradiation of visible light. The results indicate that the TiO 2 photocatalyst heat-treated at 400 °C within 60 min shows the highest photocatalytic activity which can effectively degrade the azo fuchsine under the irradiation of visible light. The remarkable improvement of photocatalytic activity of heat-treated TiO 2 powders at 400 °C was mainly illustrated by the special interphase formed between rutile and anatase phases which not only restrains the recombination of photogenerated electron–hole pairs, but also reduces the adsorbability of anatase TiO 2 powders at a certain extent. The degradation ratio of azo fuchsine in the presence of the heat-treated TiO 2 catalyst surpassed 84.36% at 3 h visible light irradiation, while the degradation ratios are only 44.2% and 64.84% for ordinary rutile and anatase TiO 2 catalysts, respectively, under the same experimental conditions. The total degradation process of azo fuchsine has been monitored by UV–vis spectra and ion chromatography. At last, the azo fuchsine molecules in aqueous solution are completely degraded and become some simple inorganic ions such as NO 3 − and SO 4 2−, etc. In this paper, the research on photocatalytic degradation kinetics was also performed and proved to be a first-order reaction.