Enhancement Of Photocatalytic Efficiency Research Articles

Photocatalytic Performance of MWCNTs/TiO2 Nanocomposites: Conventional vs. Microwave-Assisted Synthesis

Multi-walled carbon nanotubes-titanium dioxide (MWCNTs-TiO2) nanocomposites were synthesized via microwave-assisted synthesis and conventional hydrothermal method, comprising of well-crystallized anatase TiO2 nanoparticles with different MWCNTs contents. TiO2 nanoparticles synthesized by the rapid thermal decomposition of tetra-butyl titanium (Ti(OC4H9)4) in the presence of acid treated MWCNTs, were attached on the surface of MWCNTs by means of chemical bonds under microwave irradiation. The addition of MWCNTs did not influence the structure of anatase TiO2. The photocatalytic performance evaluation of composite materials was conducted under UV and visible light using methyl orange (MO) as a typical pollutant. The enhancement in photocatalytic efficiency of nanocomposites was clearly observed by the presence of MWCNTs, which could contribute to improve the adsorption of MO dye, absorption of more light and also obstruct the photogenerated electron-hole pair's recombination.

Fabrication of SubPc-Br/Ag3PO4 composites with high-efficiency and stable photocatalytic performance

Ag3PO4 has been proven to be an efficient photocatalyst to degrade organic pollutants in aqueous phase, which makes it a promising candidate for constructing an environmental purification system. In this study, novel series of subphthalocyanine-Br sensitized Ag3PO4 (SubPc-Br/Ag3PO4) photocatalysts with broadband light responsive ability were fabricated for the first time by coating SubPc-Br microcrystals onto the surface of Ag3PO4 bulk polyhedron. The obtained SubPc-Br/Ag3PO4 composites exhibited significant enhancement of photocatalytic efficiency in degrading bromophenol blue (BB) and methyl orange (MO) under both the visible-light and ultraviolet-light. It was shown that the weight percentage of SubPc-Br had a remarkable impact on the photocatalytic activities of the substrates and the 4 wt% SubPc-Br/Ag3PO4 composite displayed the most superior photocatalytic efficiency. The improved photocatalytic performance of SubPc-Br/Ag3PO4 photocatalysts could be mainly attributed to the sensitization, which broadened the absorption region and then improved the separation of photogenerated electron-hole pairs of Ag3PO4. Moreover, photo-induced electrons transfer between SubPc-Br and Ag3PO4 particles also decreased the possibility of Ag+ reduction, generating an enhanced cycling stability of SubPc-Br/Ag3PO4 photocatalysts.

Synthesis of Bi nanoparticles supported on activated carbon for efficient photocatalytic degradation of high concentration Rhodamine B

Bismuth (Bi) micro, nanoparticles are an emerging non-noble metal catalyst, but they are prone to agglomeration due to the large surface energy, which weakens its function and limits its application. Bi nanoparticles were immobilised on activated carbon by the impregnation reduction method to prevent the agglomeration. The prepared material exhibited enhanced photocatalytic efficiency compared to Bi nanoparticles alone. The origin of photocatalytic efficiency enhancement was investigated. It was attributed to the large specific surface area of the composite and more exposed active sites. This research proposes a new strategy for the photocatalytic application of Bi nanoparticles.

Construction of highly dispersed Nd2O3 nanoparticles onto mesoporous LaNaTaO3 nanocomposites for H2 evolution

Nd2O3 nanoparticles (NPs) at various contents as efficient cocatalysts were incorporated onto mesoporous LaNaTaO3 through a modified sol-gel approach for H2 evolution. The results indicated that both LaNaTaO3 and 0.6 %Nd2O3/LaNaTaO3 samples exhibited a reversible type IV adsorption isotherms characteristic for mesopores structure with large surface area around 260 m2 g–1. TEM image of Nd2O3 and LaNaTaO3 are highly dispersed with uniform semi-spherical morphology with particle size around 5 nm and 10 nm, respectively. H2 evolution over mesoporous LaNaTaO3 nanocomposite was estimated to be 1 μmolg−1; however, with boosting Nd2O3 contents from 0 to 0.6 %, the H2 evolution was increased from 1 to 1755 μmolg−1 in aqueous glycerol solution as the sacrificial reagent, it then became steady with increasing Nd2O3 above 0.6 %. The mesoporous Nd2O3/LaNaTaO3 exhibited the photocatalytic efficiency for H2 evolution 1750 times higher than LaNaTaO3. H2 evolution rate over mesoporous 0.6 %Nd2O3/LaNaTaO3 nanocomposite was greater 1420 times than that mesoporous LaNaTaO3. Photoluminescence the photoelectrochemical studies proved that the best condition amount of Nd2O3 NPs, found to be 0.6 %Nd2O3/LaNaTaO3, efficiently prohibits the photoinduced charge carriers recombination rate. It was interesting to conclude that the enhancement of photocatalytic efficiency was significantly based on the incorporation Nd2O3 NPs onto mesoporous LaNaTaO3.

Enhancement of photocatalytic pollutant decomposition efficiency of surface mounted TiO2 via lithographic surface patterning

Abstract Titanium dioxide (TiO2) based photocatalysis has been among the most popular advanced oxidation processes in environmental applications in past several decades due to its low cost, nontoxicity, and relatively high oxidizing ability, although suffering from relatively low pollutant decomposition efficiency. Here we present a study on the enhancement of efficiency of thin TiO2 film produced by reactive magnetron sputtering on an interference lithography-processed support, thus increasing the surface area. The efficiency of differently patterned samples was demonstrated by decolorization of methylene blue. The three fold enhancement of the photocatalytic efficiency was observed due to surface area enlargement, and additionally due to multiple UV light reflections.

Microwave- and Formaldehyde-Assisted Synthesis of Ag-Ag3PO4 with Enhanced Photocatalytic Activity for the Degradation of Rhodamine B Dye and Crude Oil Fractions.

The release of crude oil and water-soluble dyes into our marine environment is a major global problem. An efficient semiconductor Ag–Ag3PO4 photocatalyst was synthesized using formaldehyde as a reducing agent to form surface active Ag on Ag3PO4 under microwave radiation for heating, and its potential in destroying environmental pollutants has been examined. The diffuse reflectance spectroscopy of Ag–Ag3PO4 revealed an enhanced absorption in the visible light region. The rate of photocatalytic degradation of rhodamine B by Ag–Ag3PO4 was over 4-fold compared to Ag3PO4. The potential application of Ag–Ag3PO4 in oil spill remediation was also examined through photocatalytic degradation of benzene, n-hexane, and 1:1 v/v benzene/methanol crude oil-soluble fractions. UV–vis and gas chromatography–mass spectrometry analysis of the crude oil components after visible light irradiation showed excellent degradation. The photocatalytic efficiency enhancement of Ag–Ag3PO4 is attributed to the excellent electron trapping of silver nanoparticles deposited on the surface of Ag3PO4. This work will motivate future studies to develop recyclable visible light photocatalysts for many applications.

Novel FeWO4/WO3 nanoplate with p–n heterostructure and its enhanced mechanism for organic pollutants removal under visible-light illumination

Abstract In the first time, a novel FeWO4/WO3 p–n heterostructure was constructed through a facile two-step hydrothermal process. The optimal 0.5-FeWO4/WO3 sample exhibited 90% degradation in 2 h toward to methylene blue (MB) and tetracycline hydrochloride (TC) and the total organic carbon (TOC) removal achieved 52% and 40% with 4 h irradiated under visible light irradiation. The enhancement of photocatalytic efficiency can be attributed to the synergistic effects of higher adsorption ability, stronger visible light response, larger BET specific surface area and faster carrier separation and migration rate. The electron spin resonance (ESR) showed that the hydroxyl radical (·OH) was the primary active species. Based on the analysis of the energy band position and ESR, a possible carrier transfer mechanism of enhanced performance in the heterostructure was proposed. Furthermore, the possible degradation pathway was discussed combined with liquid chromatography mass-spectrometry (LCMS). This novel heterostructure catalyst with high efficiency may possess a promising application towards the environment issues.

Tungsten oxide-based visible light-driven photocatalysts: crystal and electronic structures and strategies for photocatalytic efficiency enhancement

Photocatalysis (PC) technology has received global attention due to its high potential of addressing both environmental and energy issues using only solar light as energy input.

P.668 Visual working memory as a possible endophenotypic schizophrenia marker

Poor efficiency of TiO2 by visible light and the fast recombination rate of electron/hole pairs remain significant challenges in photocatalytic applications of TiO2 in water treatment. In this study, graphene was used to enhance TiO2 photocatalytic activity by reducing electron-hole pair recombination. Nanocomposites were formed by combining TiO2 nanoparticles (P25) with graphene oxide (GO) though simultaneous hydrothermal synthesis and GO reduction. Nanocomposite characterization confirmed that the GO was successfully reduced and P25 nanoparticles evenly dispersed in the graphene surface. The band gap of the nanocomposite was determined to be 2.74 eV, which is a promising shift to the visible spectrum in graphene-TiO2 photocatalysts. The photocatalytic performance of the TiO2/G nanocomposites was then evaluated by quantifying the formation of 2-hydroxyterephthalic acid (HTPA) (probe molecule) under UV-LED illumination. To further optimize the photocatalytic efficiency of the TiO2/G nanocomposites, the response surface methodology (RSM) with central composite design (CCD) was used. Out of the 6 variables including stirring time, stirring speed, the amount of TiO2, the amount of GO, hydrothermal reaction time, and ethanol/water ratio, it was determined that the last three are substantially affected the HTPA formation rate. The optimum conditions were found to be GO 0.48 wt%, ethanol/water 51.49 v/V%, and a reaction time 19 h. Predicted values for HTPA formation were found to be in good agreement with experimental values (R2 = 0.93 and adj-R2 = 0.87). The optimized nanocomposite showed 125% enhancement in photocatalytic efficiency over pure P25.

Visible light driven Ni–BaMo3O10 photocatalyst for Indigo Carmine degradation: Mechanism and pathways

The microwave hydrothermal method was employed for the synthesis of Ni doped Barium trimolybdate (Ni–BaMo3O10) tripod microcrystals. The photocatalyst, BaMo3O10 and Ni–BaMo3O10 have tendency to degrade the Indigo Carmine (IC) about 40 and 98% under visible light irradiation, respectively in 180 min. The photocatalyst revealed the excellent photodegradation stability up to five cycles. The active species (OH•, O2•-, and h+) were responsible for IC degradation on the basis of scavenger test. Effect of pH on IC degradation was also investigated. The enhancement of photocatalytic efficiency for IC degradation is related to increase in visible light absorption/oxygen vacancy and efficient separation of electron-hole pairs on the surface of photocatalyst. The suppression of charge recombination explained by transient photocurrent response and EIS measurements. The IC degradation was analyzed by ultra-performance liquid chromatography-photodiode array (UPLC-PDA) and high resolution-quadruple time of flight electrospray ionization mass spectroscopy (HR-QTOF ESI/MS). The four degradation pathways of IC in water were proposed on the basis of degraded products. Hydroxylation, oxidation, methylation, decarboxylation, and desulfonation reactions were observed during IC degradation. The efficient mineralization of IC occurred according to total organic carbon (TOC) investigation. Therefore, this research article presents removal of dyes pollutants from polluted water and in-depth analysis of IC pathways.

Remarkable charge separation and photocatalytic efficiency enhancement through TiO2(B)/anatase hetrophase junctions of TiO2 nanobelts

Light harvesting and charge separation are both significant to the photocatalysis, but it is challenging to synchronously realize both in a single-component material. The surface coarsened TiO2 nanobelts with TiO2(B)/anatase hetrophase junctions and large BET surface area are prepared via a hydrothermal/annealing method. The presence of surface coarsened nanobelt structure enhances the light absorption through reflection/refraction of light. The TiO2(B)/anatase hetrophase junctions can efficiently promote the separation of photoinduced electrons and holes pairs and therefore decrease the charge recombination. The large BET surface area provides abundant active sites for the absorption and diffusion of reactants. As a consequence, the obtained TiO2 nanobelts exhibit an enhanced photocatalytic H2 evolution activity at the optimal annealing temperature (450 °C) with Pt as co-catalysts (0.786 mmol h−1g−1), exceeding that of pure anatase TiO2 nanobelts (TiO2 nanobelts-600 °C, 0.265 mmol h−1g−1). Interestingly, TiO2 nanobelts-450 °C still show a high hydrogen evolution rate of 0.601 mmol h−1g−1 in the absence of co-catalysts.

Solution mixing preparation of PVDF/ZnO polymeric composite films engineered for heterogeneous photocatalysis

ABSTRACTDespite the efforts of the scientific community, carrying out photocatalyst immobilization so that industrial application of photocatalysis becomes economically feasible is still a challenge to be overcome. In this work, polyvinylidene fluoride (PVDF)/ZnO composites were prepared by solution mixing based on solid knowledge of membrane technology and with the help of a powerful experimental design for systematic evaluation of the interaction among variables. A strategy for variable screening was used, followed by a complete evaluation at two levels, leading to predictive models. As a result, photocatalyst amount, pore agent concentration, and wet thickness were the most significant in the target molecule discoloration. With this, it was possible to obtain a 40 and 186% enhancement in photocatalytic efficiency compared to previous results and simple photolysis, respectively. Finally, the samples were characterized by FTIR‐ATR, XRD, and SEM and chemical, crystalline and morphological differences were observed both with nanoparticle and pore agent incorporation. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48417.

Photocatalytic degradation using TiO2-graphene nanocomposite under UV-LED illumination: Optimization using response surface methodology

Poor efficiency of TiO2 by visible light and the fast recombination rate of electron/hole pairs remain significant challenges in photocatalytic applications of TiO2 in water treatment. In this study, graphene was used to enhance TiO2 photocatalytic activity by reducing electron-hole pair recombination. Nanocomposites were formed by combining TiO2 nanoparticles (P25) with graphene oxide (GO) though simultaneous hydrothermal synthesis and GO reduction. Nanocomposite characterization confirmed that the GO was successfully reduced and P25 nanoparticles evenly dispersed in the graphene surface. The band gap of the nanocomposite was determined to be 2.74 eV, which is a promising shift to the visible spectrum in graphene-TiO2 photocatalysts. The photocatalytic performance of the TiO2/G nanocomposites was then evaluated by quantifying the formation of 2-hydroxyterephthalic acid (HTPA) (probe molecule) under UV-LED illumination. To further optimize the photocatalytic efficiency of the TiO2/G nanocomposites, the response surface methodology (RSM) with central composite design (CCD) was used. Out of the 6 variables including stirring time, stirring speed, the amount of TiO2, the amount of GO, hydrothermal reaction time, and ethanol/water ratio, it was determined that the last three are substantially affected the HTPA formation rate. The optimum conditions were found to be GO 0.48 wt%, ethanol/water 51.49 v/V%, and a reaction time 19 h. Predicted values for HTPA formation were found to be in good agreement with experimental values (R2 = 0.93 and adj-R2 = 0.87). The optimized nanocomposite showed 125% enhancement in photocatalytic efficiency over pure P25.

Origin of Charge Trapping in TiO2/Reduced Graphene Oxide Photocatalytic Composites: Insights from Theory.

Composites of titanium dioxide (TiO2) and reduced graphene oxide (RGO) have proven to be much more effective photocatalysts than TiO2 alone. However, little attention has been paid so far to the chemical structure of TiO2/RGO interfaces and to the role that the unavoidable residual oxygen functional groups of RGO play in the photocatalytic mechanism. In this work, we develop models of TiO2 rutile (110)/RGO interfaces by including a variety of oxygen functional groups known to be present in RGO. Using hybrid density functional theory calculations, we demonstrate that the presence of oxygen functional groups and the formation of interfacial cross-links (Ti–O–C covalent bonds and strong hydrogen bonds between TiO2 and RGO) have a major effect on the electronic properties of RGO and RGO-based composites. The electronic structure changes from semimetallic to semiconducting with an indirect band gap, with the lowest unoccupied band positioned below the TiO2 conduction band and largely localized on RGO oxygen and carbon orbitals, with some contributions of RGO-bonded Ti atoms. We suggest that this RGO-based lowest unoccupied band acts as a photoelectron trap and the indirect nature of the band gap hinders electron–hole recombination. These results can explain the experimentally observed extended lifetimes of photoexcited charge carriers in TiO2/RGO composites and the enhancement of photocatalytic efficiency of these composites.

Synergistic Effect of Dual Particle-Size AuNPs on TiO₂ for Efficient Photocatalytic Hydrogen Evolution.

Design of efficient catalysts for photocatalytic water-splitting hydrogen evolution is of fundamental importance for the production of sustainable clean energy. In this study, a dual particle-size AuNPs/TiO2 composite containing both small (16.9 ± 5.5 nm) and large (45.0 ± 9.8 nm) AuNPs was synthesized by annealing two different sized AuNPs onto TiO2 nanosheets. Dual particle-size AuNPs/TiO2 composites of 2.1 wt% catalyze photocatalytic H2 evolution 281 times faster than pure TiO2. Control experiments indicate the observed rate increase for the 2.1 wt% dual particle-size AuNPs/TiO2 composites is larger than 2.1 wt% small AuNPs/TiO2 composites, or 2.1 wt% large AuNPs/TiO2 composites in isolation. The observed photocatalytic enhancement can be attributed to the synergistic effect of dual particle-size AuNPs on TiO2. Specifically, small-sized AuNPs can act as an electron sink to generate more electron-hole pairs, while the surface plasmon resonance (SPR) effect of large-sized AuNPs concurrently injects hot electrons into the TiO2 conduction band to enhance charge transfer. In addition, a gold-dicyanodiamine composite (GDC)-directed synthesis of 2.1 wt% dual particle-size AuNPs/TiO2 composites was also completed. Notably, a photocatalytic efficiency enhancement was observed that was comparable to the previously prepared 2.1 wt% dual particle-size AuNPs/TiO2 composites. Taken together, the synergistic effects of dual particle-size AuNPs on TiO2 can be potentially used as a foundation to develop semiconductor photocatalyst heterojunction with enhanced photocatalytic activity.

Shell thickness dependent photocatalytic activity of EDTA-assisted Ag/ZnO core-shell nanoparticles under sunlight irradiation

Functionalized Ag/ZnO core–shell (CS) nanoparticles (NPs) with ethylenediaminetetraacetic acid (EDTA) having same core size but with different shell thickness are successfully prepared through a simple and low cost wet chemical process. Different physiochemical characterizations including transmission electron microscopy, x-ray diffraction, Brunauer-Emment-Teller surface area analysis, zeta potential analysis, thermal gravimetric-differential analysis, UV-visible absorption spectroscopy, Photoluminescence Spectroscopy and Fourier-transform infrared Spectroscopy have been involved to characterize the samples. The thickness of ZnO shell of Ag/ZnO CS NPs is found to be increasing with increasing molar ratio of EDTA/Zn2+. The LSPR wavelength of Ag core is shifting to longer visible wavelength with increasing the shell thickness of Ag/ZnO CS NPs because of the increase in the dielectric constant of the sourrounding environment. The increasing shell thickness of Ag/ZnO CS NPs makes a strong effect on the decrease in the fluorescence intensity of UV emission of ZnO. This quenching of PL intensity has been further verified by transient fluorescence (FL) spectra. The Nyquist plots also provide evidence of higher electron-transfer rate of the Ag/ZnO CS NPs of having higher shell thickness. The photocurrent measurement confirms electron-charging of Ag core in Ag/ZnO CS NPs. Variation of concentration of EDTA as anionic surfactant causes variation of surface charge of Ag/ZnO CS NPs. With increasing the shell thickness, photodegradation efficiency of Ag/ZnO CS NPs towards methylene blue (MB) degradation enhances under sunlight irradiation. This enhancement in photocatalytic efficiency with increasing the shell thickness is achieved due to the higher surface area, higher charge transfer efficiency, extended light absorption towards visible region and more negative zeta potential of Ag/ZnO CS NPs.

Microwave-assisted hydrothermal synthesis of BiOCl/Bi2WO6 nanocomposites for the enhancement of photocatalytic efficiency

In this research, BiOCl/Bi2WO6 nanocomposites were successfully synthesized by a microwave-assisted hydrothermal method. Phase, morphology and optical properties of the as-synthesized products were investigated by X-ray powder diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy and photoluminescence (PL) spectroscopy. The as-synthesized products were BiOCl/Bi2WO6 nanocomposites composed of Bi2WO6 microflowers mixed with BiOCl nanoplates. The photocatalytic properties of BiOCl/Bi2WO6 nanocomposites were estimated through photodegradation of rhodamine B and salicylic acid as organic models in wastewater. The 80 wt% BiOCl/Bi2WO6 nanocomposites presented the highest photocatalytic efficiency and were certified for the lowest photonic emission by PL analysis. There was a trivial loss of activity even after four re-cycle tests. A mechanism for photocatalysis by BiOCl/Bi2WO6 nanocomposites was also proposed.

Bio‐Inspired Plasmonic Photocatalysts

AbstractThe conversion of solar energy to sustainable energy sources is a significant field of study for the relief of the world's energy problems, and among the various strategies developed, semiconductor photocatalysts have received significant attention as a promising candidate due to their attractive efficiency, mild reaction conditions, and low cost. The enhancement of such photocatalysts with plasmonic materials, by virtue of the Schottky junction and localized surface plasma resonance phenomenon, could facilitate the rapid progress in enhancement of photocatalytic efficiency under visible light irradiation. To further improve photocatalytic efficiency, scientists look to nature for inspiration, culminating in the evolution of complex hierarchical structures in order to fully utilize the potential of solar energy. In the past decade, there has been significant progress in the development of bio‐inspired plasmonic photocatalysts, such as antireflective surfaces, 3D photonic structures, and branched structures. This review describes the state‐of‐the‐art bio‐inspired light manipulation approaches, as well as future challenges in solar energy harvesting by plasmonic photocatalysts.

Dimensional Impact of Metal–Organic Frameworks in Catalyzing Photoinduced Hydrogen Evolution and Cyanosilylation Reactions

Metal–organic frameworks (MOFs) have been widely studied as heterogeneous catalysts. Compared to the MOFs with three-dimensional (3D) topologies, two-dimensional (2D) MOF nanosheets can allow facile access to the active sites on their external surface, thus having huge potentials in catalysis. Herein, we fabricate 2D MOF nanosheets, UiO-67-NS, as photocatalyst for H2 evolution reaction, and study their photocatalytic performance in relation to their 3D bulk counterparts (UiO-67). The UiO-67-NS exhibit an 84-fold increase in photocatalytic efficiency compared to UiO-67. Postsynthetic cation grafting of the UiO-67-NS with titanium leads to further enhancement in photocatalytic efficiency, giving a hydrogen evolution rate of up to 393 μmol g–1 h–1, which is 13-times higher than that of the nongrafting nanosheets under the same condition. Our results indicate that the 3D-to-2D dimensionality reduction can be a viable strategy for the development of MOFs as efficient photocatalysts. In addition, we have demons...

Solar activation of TiO2 intensified with graphene for degradation of Bisphenol-A in water

Photocatalytic degradation of a Bisphenol-A (BPA) aqueous solution was achieved using titanium dioxide (TiO2) and graphene-based TiO2 photocatalysts activated by solar light. First, a comparative study of the adsorption kinetics of BPA, in the presence of both catalysts, as a function of pH was performed. Then, the effect of the initial BPA concentration and catalyst loading was assessed and the optimal conditions for BPA degradation by means of heterogeneous solar photocatalysis were determined. It was observed that TiO2 modified with 2 wt% graphene improved the photocatalytic efficiency in terms of BPA mineralization. The TiO2/graphene photocatalytic composite achieved a 16% increase in the photocatalytic mineralization of the BPA solution under solar light compared to un-doped TiO2. This enhancement of photocatalytic efficiency is a result of the increase of active sites for BPA adsorption, the more efficient harvesting of solar light, and the inhibition of electron-hole recombination. The dynamic behavior of hydroxyl radicals and dissolved oxygen in these systems was also discussed. Finally, the roles played by hydroxyl radical, HO, superoxide radical anion, O2−, and singlet molecular oxygen, 1O2, were studied in both TiO2 and TiO2/graphene systems. It was found that O2− were the main oxidative species in both systems.