Efficient Visible-light Photocatalyst Research Articles

Construction of 3D sponge-like hierarchical pore Ag10Si4O13 microblock photocatalyst with enhanced photocatalytic activities

Designing efficient visible light photocatalysts is targeted to improve the solar utilization to ameliorate environmental problems. Ag10Si4O13 has great application potential due to a narrow band gap and the existence of internal electric field（spontaneous polarization electric field inside the crystal）. Here, a novel and convenient synthetic strategy based on sol-gel method and template method was proposed to fabricate 3D sponge-like hierarchical pore Ag10Si4O13 (HPA) microblock with enhanced photocatalytic activities. The group multiple coordination is conducive to further improve the dispersion of Ag10Si4O13 precursor around polystyrene (PS) microsphere. Weak sintering between nano-Ag10Si4O13 particles ensured the formation of sponge skeleton structure. Compared with Ag10Si4O13, HPA showed enhanced separation efficiency of electron hole pairs due to the carbon doping. And the uniform and well-developed pore structures further improved the photocatalytic performance. As a result, HPA (P-5) exhibited a degradation efficiency of 98.98% at 30 min under visible light, and an excellent cycle performance were obtained. The proposed strategy provides an important reference for the preparation of easily recoverable microblock photocatalyst.

Recoverable and reusable visible-light photocatalytic performance of CVD grown atomically thin MoS2 films

The decomposition of water pollutants including industrial dyes and chemicals via photocatalytic decontamination is one of the major investigated problems in recent years. Two-dimensional molybdenum disulfide (MoS2) layers have shown great promise as an efficient visible-light photocatalyst owing to its numerous active sites and large surface area. In this study, atomically thin MoS2 films of different thicknesses from monolayer to five-layer and ten layers were fabricated on sapphire substrates using chemical vapor deposition (CVD). We demonstrate that these MoS2 thin films can be used as a photocatalyst to degrade Methylene Blue (MB) dye and can be recovered completely with utmost structural and chemical stability. Under visible-light irradiation, the MB absorption peak completely disappears with ∼95.6% of degradation after 120 min. We also demonstrate the reusability of the MoS2 thin films without significantly losing the photocatalytic activity even after 5-cycles of degradation studies. The chemical and structural stability of the MoS2 films after 5-cycles of degradation studies were affirmed using various spectroscopic studies. Our findings suggest that the MB degradation efficiency increases from 19.01% to 98.46% with an increase in pH from 4 to 14. Our approach may facilitate a further design of other transition metal dichalcogenides-based recoverable photocatalysts for industrial applications.

S-doped carbon nanosheets supported ZnO with enhanced visible-light photocatalytic performance for pollutants degradation

The exploration of highly efficient and stable visible-light-driven photocatalysts remains a great challenge for organic pollutant management. Herein, a novel S-doped carbon nanosheet (SCN)/ZnO composite photocatalyst has been synthesized via a facile method using the freeze-drying cellulose nanocrystals (CNCs) as the carbon precursor. The surface morphology and chemical environment of SCNs can be regulated simultaneously with S-doping. Compared to the pristine carbonized CNCs (CN), the SCN carbonized at 550 °C (SCN-550) has regular nanosheet-like morphology, integrated graphitic structures (ID/IG of 0.692), rich surface heteroatoms (14.62 at% for O, 1.93 at% for S), and most content of oxidized-S atoms (100 at%). It endows the increased surface reactive sites (specific surface area of 45.55 m2 g−1), accelerated electron transfer, enhanced visible-light absorption, and prolonged carrier lifetime for the corresponding SCN-550/ZnO composite. Consequently, the SCN-550/ZnO shows an outstanding photocatalytic performance for methylene blue (99%). In addition, SCN-550/ZnO composite exhibits general application to organic contaminants, including phenol (91%), formaldehyde (92%), acetone (79%), and methyl alcohol (84%), respectively. Furthermore, the strong interaction of Zn–O–C covalent bond between SCN-550 and ZnO ensures the high photocatalytic activity of SCN-550/ZnO composite after four cycles, demonstrating its excellent reusability and stability. This study develops a highly efficient visible-light photocatalyst of CNCs derived S-doped carbon nanosheets supported ZnO for environment purification.

Au nanoparticles decorated polypyrrole-carbon black/g-C3N4 nanocomposite as ultrafast and efficient visible light photocatalyst

Modification and bandgap engineering are proposed to be extremely significant in improving the photocatalytic activity of novel photocatalysts. The current research focused on the fabrication of ultrafast and efficient visible light-responsive ternary photocatalyst containing g-C3N4 nanostructures in conjugation with polypyrrole doped carbon black (PPy-C) and gold (Au) nanoparticles by highly effectual, simple, and straightforward methodology. Various analytical techniques like XRD, FESEM, TEM, XPS, FTIR, and UV–Vis spectroscopy were applied for characterization purposes. The XRD and XPS results confirmed the successful creation of a nanocomposite framework among Au, PPy-C and g-C3N4. The TEM images revealed that bare g-C3N4 holds sheets or layered graphitic structure with sizes ranging from 100 to 300 nm. The sponge-like PPy-C network intermingled perfectly with g-C3N4 sheets along with homogeneously distributed 5–15 nm Au nanoparticles. The band gap energy (Eg) for bare g-C3N4, PPy-C/g-C3N4 and Au@PPy-C/g-C3N4 nanocomposites were found to be 2.74, 2.68, and 2.60 eV, respectively. The photocatalytic activity for all newly designed photocatalysts have been assessed during the degradation of insecticide Imidacloprid and methylene blue (MB) dye, where Au@PPy-C/C3N4 was found to be extremely efficient with ultrafast removal of both imidacloprid and MB in just 25 min of visible light irradiation. It was revealed that the Au@PPy-C/g-C3N4 ternary photocatalyst removed 96.0% of target analyte imidacloprid, which is ⁓ 2.91 times more efficient than bare g-C3N4 in treating imidacloprid. This report provides a distinctly promising, highly effectual and straightforward route to destruct extremely toxic and notorious pollutants and opens a new gateway in the present challenging scenario of environmental concerns.

Double perovskite nanostructured Dy2CoMnO6 an efficient visible-light photocatalysts: synthesis and characterization

Double perovskite nanostructured Dy2CoMnO6 an efficient visible-light photocatalysts: synthesis and characterization

Anchoring dye onto 1D Nb2O5 in cooperation with TEMPO for the selective photocatalytic aerobic oxidation of amines

Visible light-driven photocatalysis over semiconductors has emerged as one of the most desired strategies for animating diverse selective chemical transformations. Herein, one-dimensional (1D) Nb2O5 nanorods with a specific surface area of 264 m2•g−1 were synthesized via a straightforward hydrothermal method. Thereafter, an efficient visible light photocatalyst was constructed by in-situ anchoring of alizarin red S (ARS) onto the Nb2O5 nanorods to afford ARS-Nb2O5. Resultantly, the ARS-Nb2O5 nanorods can facilitate the selective aerobic oxidation of amines into imines, affording about twice of the result over 3D hierarchical Nb2O5. Notably, 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) could synchronize the intricate electron and proton transfers between ARS-Nb2O5 nanorods, amines, and superoxide (O2•−). In most cases, the green light-driven primary and secondary amines into imines could be completed with about 95% selectivity within 2 h. This work highlights the dimension of designing semiconductor materials to anchor visible light-active molecules for selective oxidation reactions under benign conditions.

Ag3PO4-TiO2-Carbon nanofiber Composite: An efficient Visible-light photocatalyst obtained from electrospinning and hydrothermal methods

In this contribution, we synthesized Ag3PO4-TiO2 NPs assembled carbon nanofibers (Ag3PO4-TiO2-CNFs) photocatalyst by the combination of electrospinning and hydrothermal processes. The photocatalyst was characterized by various techniques such as SEM, TEM, XRD, UV, PL, etc. The morphological examination by SEM and TEM revealed a uniform distribution of the Ag3PO4 NPs over the TiO2-CNFs surface. Compared to TiO2 NFs, the loading of Ag3PO4 NPs into the TiO2-CNFs composite enhances its absorbance to the visible light region and offers a route with low resistance for charge separation. The photocatalytic performance of the Ag3PO4-TiO2-CNFs composite was studied by a methylene blue (MB) degradation test under visible light irradiation. It was observed that the Ag3PO4-TiO2-CNFs composite exhibited significantly enhanced photocatalytic performance as compared to the pristine Ag3PO4 NPs and TiO2 NFs. The Ag3PO4-TiO2-CNFs composite eliminated the entire MB dye within 10 min of visible light irradiation. Also, the reusability test indicated that the photocatalyst possesses excellent stability. The high photocatalytic activity is attributed to the increased surface area, enhanced visible light response, accelerated charge separation, and dye adsorption property of the composite material. Furthermore, the photocatalyst showed good antibacterial property against Escherichia coli (E. coli) bacteria. The excellent dyes removal ability and the good antibacterial property of the as-prepared Ag3PO4-TiO2-CNFs photocatalyst show the potentiality of the material in wastewater treatment.

Surface engineering of copper sulfide-titania-graphitic carbon nitride ternary nanohybrid as an efficient visible-light photocatalyst for pollutant photodegradation

Advanced photocatalyst is a key for photocatalytic water purification in the environmental pollutant remediation. In this study, graphitic carbon nitride (g-CN) modified by CuS and TiO2 ternary nanohybrid (CuS-TiO2-g-CN) with close interfacial contact among CuS, TiO2 and g-CN was fabricated through a facile and green method. Compared to the binary g-CN-based counterparts, the CuS-TiO2-g-CN possesses multiple photo-generated charge transfers owing to the synergistic action of CuS, TiO2 and g-CN. And hence the separation efficiency of photo-generated electron-hole pairs can be improved for the CuS-TiO2-g-CN. The optical and photoelectrochemical measurements prove that the CuS-TiO2-g-CN has narrower band gap energy and higher transient photocurrent density than those of g-CN and TiO2-g-CN. Therefore, the CuS-TiO2-g-CN shows notably higher photocatalytic activity and stability towards the degradation of Rhodamine B (RhB) than g-CN and TiO2-g-CN under visible-light irradiation. Moreover, a possible visible-light photocatalytic mechanism of CuS-TiO2-g-CN for degrading RhB was also proposed on the basis of the experimental results and literature reports.

Selective photocatalytic formation of sulfoxides by aerobic oxidation of sulfides over conjugated microporous polymers with thiazolo[5,4‑d]thiazole linkage

Developing selective formation of sulfoxides by aerobic oxidation of sulfides over highly efficient visible-light photocatalysts is an essential but challenging task. Herein, a conjugated microporous polymer (CMP) photocatalyst with the desired linkage thiazolo[5,4‑d]thiazole (TzTz) is presented to undertake this task. Remarkably, a catalyst-free solvothermal process afforded TzTz-CMP-3 from tetra(4-formylphenyl)-benzene and dithiooxamide. The photocatalytic activity of TzTz-CMP-3 is demonstrated with the blue light-powered selective formation of sulfoxides by aerobic oxidation of sulfides. A wide range of sulfoxides can be effectively formed by oxidation of sulfides with excellent product selectivities (up to 99 %) over the TzTz-CMP-3 photocatalyst. The more symmetric π-conjugated aromatic ring of TzTz-CMP-3 endows it with more favorable activity than the less symmetric ones. This work underscores the symmetry of building blocks for CMPs for selective photocatalytic formation of valuable organic molecules.

A composite of graphene-beaded porous carbon-nanofibers and TiO2 nanoparticles as an efficient visible-light photocatalyst

Novel composites of graphene-beaded porous carbon nanofibers decorated with TiO2 (G/PCF/TiO2) were synthesized using an electrospinning method and their photocatalytic performance was demonstrated based on the degradation of methylene blue (MB) under visible light irradiation. The enhanced photocatalytic properties of G/PCF/TiO2 can be ascribed to the synergistic effect of graphene-beaded porous carbon nanofibers, which facilitates charge transfer, increases the light absorption in the visible range, as well as favors the adsorption of dye. The present strategy provides an effective strategy for the preparation of carbon-based composite and its application for high-performance photocatalysts.

Transformation of CuS/ZnS nanomaterials to an efficient visible light photocatalyst by 'photosensitizer' graphene and the potential antimicrobial activities of the nanocomposites.

We report the growth of CuS/ZnS (CZS) nanoparticles (NPs) on the graphene sheet by a facile green synthesis process. The CuS/ZnS-graphene (CZSG) nanocomposites exhibit enhanced visible light photocatalytic activity towards organic dye (methylene blue) degradation than that of CZS nanoparticles. To find the reason for the enhanced photo-activity, we propose a new photocatalytic mechanism where graphene in the CZSG nanocomposites acts as a 'photosensitizer' for CZS nanoparticles. This distinctive photocatalytic mechanism is noticeably different from all other previous research works on semiconductor-graphene hybrid photocatalysts where graphene behaves as an electron reservoir to capture the electrons from photo-excited semiconductor. This novel idea of the photocatalytic mechanism in semiconductor-graphene photocatalysts could draw a new track in thinking for designing of graphene-based photocatalysts for solving environmental pollution problems and they also show remarkable antimicrobial activities.

Improvement of Photocatalytic Activity of Bi2WO6 by Doping Ag and Y: A DFT Study

Although much attention has been recently focused on Bi2WO6 and doping materials as highly efficient visible-light photocatalysts, the selection of an appropriate element as dopant and our understanding of the photocatalytic mechanism from the electronic level still need to be further investigated. In the current work, electronic band structures, density of states, optical properties, and effective mass for Bi2WO6, Ag-doped Bi2WO6 and Y-doped Bi2WO6 semiconductors have been studied by density functional theory calculations. We find that, while both the doped systems show little change in the band gap from Bi2WO6, Ag-doped and Y-doped Bi2WO6 produce more dispersive bands compared to the original Bi2WO6, implying that the doped systems can facilitate the spatial separation of photo-induced electron–hole pairs, and thus enhance the photocatalytic performance. In addition, for Ag-doped Bi2WO6, the presence of an Ag impurity energy band just above the valence band is expected to act as electron-trapping sites leading to a reduction of the recombination rate of photogenerated carriers. Our findings could provide an explanation for the experimental observations reported in the literature.

Interface of GO with SnO2 quantum dots as an efficient visible-light photocatalyst

Graphene oxide (GO) with beneficial functional groups regulates the surface chemistry for catalytic applications. However, the low electrical conductivity of GO invokes further treatments that compromise the above-valued properties. We report an interfacial engineering of GO decorated with SnO2 quantum dots (QDs) for the visible-light-driven catalysis of dye degradation. Retention of beneficial functional features of GO and QDs in the GO-SnO2 composite is established by using TEM, FTIR, and Raman spectroscopy techniques. Further, investigations with EXAFS and lifetime-measurements provide the local structure and defects distributions in QDs which are correlated with the improved conductivity. PL and electrochemical impedance spectroscopic measurements help unraveling the charge-transfer across the interface of the GO-SnO2 composite. The unique ability of ∼94% degradation of MB using only 0.5 mg of GO-SnO2 catalyst within half an hour under the visible light is demonstrated for the first time with insights on the photocatalytic mechanism.

Graphene oxide–ZnO nanocomposite: an efficient visible light photocatalyst for degradation of rhodamine B

Lignin-based graphene oxide (L-GO), zinc oxide (ZnO), and modified L-GO–ZnO nanocomposites are prepared to explore the photocatalytic efficiency of the catalysts under UV–visible light irradiation. The absorbance of dye’s solution (rhodamine B) at regular intervals has been recorded at λmax = 553 nm using a UV–Vis spectrophotometer. The kinetics parameters, viz. half-life (t1/2), time constant τ (Tau), and rate constant (k), have been evaluated by integrated rate expression to predict the order of the reaction. The rate constant for the reactions has been evaluated to be k_L-GO–ZnO = 1.46 × 10–1, k_ZnO = 2.23 × 10–2, and k_L-GO = 1.740 × 10–2 min−1. The degradation reaction is predicted to follow the first-order kinetics when the data are fitted to the integrated rate expression, kt = -ln(D/D0). The interactions of the dye and the catalyst have been probed by FTIR spectroscopy. The percent degradation efficiency of ZnO, L-GO, and L-GO–ZnO catalyst is 85.96, 83.15, and 91.75, respectively.

Synthesis of Au/UiO-66-NH2/Graphene composites as efficient visible-light photocatalysts to convert CO2

The production of new solar fuel through CO2 photocatalytic reduction has aroused tremendous attention in recent years because of the increased demand of global energy sources and global warming caused by the mass concentration of CO2 in the earth's atmosphere. In this work, UiO-66-NH2 was co-modified by the Au nanoparticles (Au-NPs) and Graphene (GR). The resultant nanocomposite exhibits a strong absorption edge in visible light owing to the surface plasmon resonance (SPR) of Au-NPs. More attractively, Au/UiO-66-NH2/GR displays much higher photocatalytic activity (49.9 μmol) and selectivity (80.9%) than that of UiO-66-NH2/GR (selectivity: 71.6%) and pure UiO-66-NH2 (selectivity: 38.3%) for the CO2 reduction under visible light. The enhanced photocatalytic performance is primarily dued to the surface plasmon resonance (SPR) of Au-NPs, which could enhance the visible light absorption. The GR sheets could play as an electron acceptor with superior conductivity and thus suppress the recombination of electrons and holes. Besides, the GR could also improve the dispersibility of UiO-66-NH2 so as to expose more active sites and strengthen the capture of CO2. The contact effect and synergy effect among different samples are strengthened in the ternary composites and the photocatalytic performance is therefore improved. This study demonstrates a MOF based hybrid composite for efficient photocatalytic CO2 reduction, the findings not only prove great potential for the design and application of MOFs-based materials but also bring light to novel chances in the development of new high performance photocatalysts.

Fabrication of Ag decorated g-C3N4/LaFeO3 Z-scheme heterojunction as highly efficient visible-light photocatalyst for degradation of methylene blue and tetracycline hydrochloride

The discharge of industrial wastewater poses serious concerns to the environment and human health. Therefore, urgent development of simple and efficient catalysts for removal of pollutants is required. In this study, a novel ternary nanocomposite Ag/g-C3N4/LaFeO3 (A/CN/LFO) was synthesized for the degradation of dye and pharmaceutical wastewater. The catalyst was prepared by decorating Ag nanoparticles (NPs) on g-C3N4/LaFeO3 (CN/LFO) Z-scheme heterojunction and formation of Schottky junctions with LaFeO3 (LFO) and g-C3N4 (CN). The formed hybrid structure between metal and Z-scheme heterojunction induced directional transfer of electrons or holes from the Z-scheme heterojunction to metal, providing maximum separation between electrons and holes for more efficient redox reactions. Consequently, the ternary nanocomposite displayed optimized efficiencies toward the photocatalytic degradation of methylene blue (MB) and tetracycline hydrochloride (TC) under visible-light irradiation, estimated to 98.97% (90 min) and 94.93% (120 min), respectively. These values were almost 4.81 times and 3.88 times higher than those of pristine LaFeO3, respectively. The charge transfer mechanism and pollutant degradation pathway were also studied. The data revealed that Ag decorated Z-scheme heterojunction showed efficient light absorption and separation of photogenerated carriers, which might be useful for large-scale practical applications related to wastewater treatment and pollution control.

Visible light sensitive hexagonal boron nitride (hBN) decorated Fe2O3 photocatalyst for the degradation of methylene blue

The role of the carbon-based two-dimensional (2D) structures such as graphene or graphene oxide on the properties of metal oxide/2D composites materials are extensively studied for the environmental applications like photocatalysis. However, the metal oxide/inorganic 2D structure-based composites are less explored. In this regard, we have explored the α-Fe2O3/inorganic 2D hexagonal boron nitride (hBN) composite as an efficient visible light photocatalyst for the degradation of methylene blue (MB). A systematic investigation on the role of varying the weight percent of hBN on the photocatalytic efficiency for MB degradation under visible light was studied. The α-Fe2O3/(x) hBN (x = 1, 5, 10 wt%) composites were characterized by various analytical and spectroscopic techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The bandgap tuning with varying compositions of α-Fe2O3/(x) hBN (x = 1, 5, 10 wt%) were investigated by UV–vis diffuse reflectance spectroscopy (UV DRS) and the bandgap values were found to decrease with addition of hBN (1.56 eV for 5 wt%) compared to bare α-Fe2O3 (2.02 eV). The composite α-Fe2O3 with 5 wt% of hBN (FB2) showed an enhanced methylene blue (MB) degradation of ~ 91% with a high rate constant value of 5.03 × 10–4 s−1. This was ~ 3.3 times higher than the rate constant observed for the MB degradation using bare hematite. The material after photocatalysis process was retrieved by simple sedimentation process and reused for four cycles with no loss in degradation efficiency. The as-prepared composite material may have application in recycling and reuse of water in textile industries.

Heterogeneous photocatalytic degradation of organic dyes by highly efficient GdCoSnO3

The influence of calcination temperature on the photocatalytic activity of quaternary metal oxide nanocomposite i.e. gadolinium (Gd) doped cobalt tin oxide (CoSnO3) have been explored. The synthesis of nanocomposite material was completed in two steps using a novel method. The synthesized nanocomposite material was subjected to various characterization techniques like thermogravimetric analysis (TGA), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), particle size analyzer (PSA), UV–Visible and photoluminescence spectroscopy in order to investigate its thermal, structural, and optical properties. The crystallite size, particle size and optical band gap estimated via XRD, PSA and UV–Visible spectroscopy, respectively reveals an increasing trend with calcination temperature. The Gd doped CoSnO3 nanocomposite material is found to be very efficient visible light photocatalyst. The photo-degradation efficiency in the presence of sunlight in degrading methylene blue and methyl orange is more than 90%. An insight mechanism of electron/hole trapping using electronic configuration has also been explored.

In situ synthesis of holey g-C3N4 nanosheets decorated by hydroxyapatite nanospheres as efficient visible light photocatalyst.

The interesting g-C3N4 nanosheet morphology has drawn huge attention in photocatalytic applications because of its special features. Nonetheless, the relative activity of these nanosheets is still controversial due to the low available active sites and the high recombination probability of photo-induced charge carriers. In this work, in situ sol–gel approach was applied to synthesize holey g-C3N4 nanosheets/hydroxyapatite (HAp) nanospheres with plentiful in-plane holes. Herein, the presence of Ca2+ plays a key role in the formation of holey defects on 2D g-C3N4. In-plane holes provide nanosheets with more active edges and diffusion channelsv, resulting in a tremendous enhanced mass and photo-induced charge transfer speed. Moreover, the holes make highly numbered boundaries, which lead to the prevention of aggregation. On the other hand, distributed nano-HAp spheres on these nanosheets can form effective heterojunctions having high photo-degradation ability of pollutants. Intrinsic O-vacancies inside HAp unit cells mainly affect the capture of photogenerated electrons, pollutant molecules, and O2 gas. The synergistic presence of O-vacancies and holey defects (C-vacancies) on 2D g-C3N4 plays a key role in raising the photocatalytic performance of holey g-C3N4/HAp. It can be concluded that the proposed preparation method is a promising approach for simultaneous synthesis of holey g-C3N4 and surface heterojunctions of Ca-based materials. This new structure has shown significant degradation ability of bisphenol A, a prominent pollutant, with a low amount (0.01 g) and short time.

Stable lead-halide perovskite quantum dots as efficient visible light photocatalysts for organic transformations.

Lead halide perovskite (LHP) based colloidal quantum dots (CQDs) have tremendous potential for photocatalysis due to their exceptional optical properties. However, their applicability in catalysis is restricted due to poor chemical stability and low recyclability. We report halide-passivated, monodisperse CsPbBr3CQDs as a stable and efficient visible-light photocatalyst for organic transformations. We demonstrate oxidative aromatization of a wide range of heterocyclic substrates including examples which are poor hydrogen transfer (HAT) reagents. Two to five-fold higher rate kinetics were observed for reactions catalyzed by CsPbBr3CQDs in comparison with bulk-type CsPbBr3 (PNCs) or conventionally synthesized CsPbBr3CQDs and other metal organic dyes (rhodamine 6G and [Ru(bpy)3]2+). Furthermore, these CQDs exhibit improved air-tolerance and photostability and in turn show a higher turnover number (TON) of 200, compared to conventionally prepared CQDs (TON = 166) and state-of-the-art bulk-type perovskite-based catalyst (TON = 177). Our study paves the way for the practical applicability of energy-level tunable, size-controlled LHP CQDs as efficient photocatalysts in organic synthesis.