Visible Light Harvesting Ability Research Articles

In-situ route for the graphitized carbon/TiO2 composite photocatalysts with enhanced removal efficiency to emerging phenolic pollutants

AbstractTiO2 is the most photoactive material because of its superstrong photooxidizing ability, and TiO2 photocatalysis has been widely applied in sustainable water treatment and environmental remediation. However, poor sunlight or visible-light harvesting efficiency and fast recombination rate of the photogenerated charge carriers severely limit the practical applications of TiO2. To overcome these problems, the present work demonstrates a facile in-situ co-condensation method combined with hydrothermal treatment to prepare a series of graphitized carbon/TiO2 composite photocatalysts, and anatase TiO2 phase and π-π-conjugated polycyclic aromatic carbon structure are created simultaneously. As-prepared TiO2/C composites exhibit remarkably high visible-light photocatalytic activity in the degradation of aqueous emerging phenolic pollutants, acetaminophen (APAP) and methylparaben (MPB), and apparent rate constant of the TiO2/C composite with carbon doping level of 10.3% for APAP and MPB removal is 7.6 and 2.8 times higher than that of bare TiO2, and 6.2 and 2.6 times higher than that of Degussa P25 TiO2. Based on the results of photoelectrochemical experiments, indirect chemical probe measurements, and ESR spectroscopy, it is verified that doping TiO2 with graphitized carbon is responsible for this enhanced photocatalytic activity, which renders the improved visible-light harvesting ability, the accelerated separation of the photogenerated charge carriers, and enlarged BET surface areas. Through analyzing the intermediates yielded in the photodegradation process, the pathway of visible-light photocatalytic degradation of APAP and MPB over the TiO2/C composite is proposed.

Boosting the photoreduction activity of Cr(vi) in metal–organic frameworks by photosensitiser incorporation and framework ionization

The Cr(VI) photoreduction efficiency in a Zr-based MOF is largely boosted by photosensitizer introduction and framework ionization, resulting from the great improvement of both the visible light harvesting ability and Cr(vi) adsorption performance.

A rhenium catalyst with bifunctional pyrene groups boosts natural light-driven CO2 reduction

A rhenium–pyrene catalyst that dramatically promotes sunlight-induced CO2RR efficiency was developed by enhancing intermolecular electron transfer efficiency and visible light-harvesting ability.

<i>In Situ</i> Solvothermal Synthesis of CdS-Bi <sub>2</sub>MoO <sub>6</sub> Core-Shell Heterostructures with Enhanced Photocatalytic Performance Under Visible Light

Herein, we report the in situ solvothermal synthesis of CdS-Bi2MoO6 core-shell heterostructures (CdS-Bi2MoO6 CSHs) for the photocatalytic elimination of methyl orange (MO) under visible light. The as-synthesized CdS-Bi2MoO6 CSHs exhibited highest photocatalytic performance of 98.5%, which is approximately 10 and 4 folds higher than pristine Bi2MoO6 nanosheets (NSs) and CdS nanorods (NRs), respectively. This significantly enhanced photocatalytic performance is attributed to the core-shell heterostructeure that improves the visible-light harvesting ability, facilitates efficient separation and transfer of the photogenerated charge carriers, as well as synergistic band alignment of both CdS NRs and Bi2MoO6 NSs. The hole (h+) and superoxide radical anion (•O2−) were determined to be the predominant active species accountable for the MO dye degradation. Furthermore, the CdS-Bi2MoO6 CSHs exhibited a satisfactory recycling efficiency over five cycles (reduced by approximately 6%), owing to the protective Bi2MoO6 shell over the CdS NR core, demonstrating their applicability in wastewater purification.

One‐step synthesis of a WO3‐CuS nanosheet heterojunction with enhanced photocatalytic performance for methylene blue degradation and Cr(VI) reduction

AbstractBACKGROUNDThe photocatalytic activity of a pristine semiconductor is unsatisfactory due to the rapid recombination of photogenerated electrons and holes. Constructing composite photocatalysts has proven to be an effective method to suppress electron–hole recombination. The composites composed of two materials usually are synthesized through a two‐step process. However, in this work, a simple one‐step solvothermal method employing an homogeneous reaction system was adopted to synthesize a tungsten trioxide (WO3)‐copper sulfide (CuS) nanosheet heterojunction with enhanced photocatalytic properties.RESULTSThe formation of the WO3‐CuS heterojunction was confirmed by X‐ray diffraction, transmission electron microscopy, energy‐dispersive X‐ray and X‐ray photoelectron spectroscopy analysis. The composites showed improved visible light harvesting ability, and enhanced photoelectric and photocatalytic properties compared with pure WO3. The optimized composite displayed a photocurrent almost five‐fold greater than the sum of the photocurrents of WO3 and CuS, and had superior performance for methylene blue (MB) degradation and hexavalent chromium [Cr(VI)] reduction. The MB degradation and Cr(VI) reduction efficiencies were both improved when they co‐existed in the photocatalytic system. Interferential ions Cl− and NO3− were much less effective in the degradation of MB than in the reduction of Cr(VI).CONCLUSIONSImproved photocatalytic activity was achieved after coupling CuS with WO3, due to the enhanced visible light absorption and efficient electron–hole separation. Photogenerated holes were found to be the dominant reactive species in the MB photodegradation process. A synergistic effect existed between MB degradation and Cr(VI) reduction. Interferential ions Cl− and NO3− had much greater effect on Cr(VI) reduction than MB degradation. © 2019 Society of Chemical Industry

Synthesis of a heterojunction CoTiO3/Co3O4 nano-composite thin film with superior photocatalytic activity and reusability: Effect of calcination temperature on phase transformation and effect of oxidants on enhanced degradation of Indo Light Blue dye.

CoTiO3/Co3O4 heterojunction nano-composite was grown by a coprecipitation method at low temperature. The effects of calcination temperature on the phase composition, crystallization and morphology of the cobalt titanates were also examined. Notably, the novel nano-crystalline cobalt titanate with a narrow band gap to coulpe with cobalt oxide (Co3O4) by a direct coprecipitation method (CoTiO3/Co3O4) was attained. The Nano-crystalline samples were systematically characterized by TG/DTG, XRD, DRS, FESEM, FT-IR, EDX and XPS techniques. The results showed that CoTiO3/Co3O4 nano-composite hetero-junction was formed at 650°C, while at 750°C a single phase CoTiO3 nano-crystal was prepared. Photocatalytic activities indicated the heterostructured CoTiO3/Co3O4 nano-composite exhibited much higher photocatalytic activity for degradation of Indo Light blue under visible light irradiation with added oxidants (K2S2O8, KBrO3, and H2O2). The charge separation of CoTiO3 and Co3O4 would result the enhanced visible-light harvesting ability and longer lifetime of photogenerated charge carriers. The stability and reusability of catalysts during four successive cycles were resulted. Finally, a possible mechanism responsible for the charge separation and improved photocatalytic activity was proposed.

Exploration of a novel Type II 1D-ZnO nanorods/BiVO4 heterojunction photocatalyst for water depollution

In this study, we reported on the successful fabrication of a novel heterojunction photocatalyst (in particulate system) with a Type II band alignment between 1D-ZnO nanorods and BiVO4 nanocrystals. Pristine 1D-ZnO nanorods and BiVO4 nanocrystals were first fabricated through hydrothermal reaction followed by heterojunction formation via the wet chemical reaction. The 1D-ZnO/xBiVO4 heterojunction photocatalyst (x=weight ratio of BiVO4 in g) that found optimum when x=0.08g was used for the degradation of salicylic acid (SA) and Reactive Black 5 (RB5) resulting in high pseudo-first-order reaction rate constants of 0.0049min−1 and 0.0132min−1, respectively. Electrochemical studies proved that the 1D-ZnO/0.08BiVO4 heterojunction photocatalyst demonstrated a fast charge mobility and the most efficient photogenerated charge carriers separation among other heterojunction samples as analysed from PL spectra. Besides, UV–vis spectroscopic measurement and optical characterisation showed that the improved photoactivity in 1D-ZnO/BiVO4 is attributed to the formation of a Type II heterojunction staggered arrangement that enables a broader visible-light harvesting ability. Finally, a postulation photocatalytic mechanism was proposed based on the theoretical band alignment diagram between the 1D-ZnO nanorods and BiVO4 nanocrystals as well as portraying the fundamental charge carriers transfer within the 1D-ZnO/BiVO4 heterojunction photocatalyst.

Black phosphorus/graphitic carbon nitride: A metal-free photocatalyst for “green” photocatalytic bacterial inactivation under visible light

In the drive toward the ever-increasing standards for high-quality drinking water, exploring stable and efficient photocatalysts with excellent visible light (VL) harvesting ability for the photocatalytic water disinfection is still a challenging problem. However, most photocatalysts are solely metal-based or contain at least one metal-containing cocatalyst with detrimental environmental impacts. Here, we show that a novel metal-free 2D heterostructure (BP-CN) composed of black phosphorus (BP) and graphitic carbon nitride (CN) can be used as a VL-driven photocatalyst to achieve highly efficient water disinfection. The activity of BP-CN photocatalyst was about 7 times better compared with that of pure CN for the disinfection of indicator bacteria, with the complete inactivation of bacterial cells (107 cfu·mL−1) within 60 min. The bacterial inactivation mechanism was thoroughly investigated, and hydroxyl radical (OH) and H2O2 were determined to be the major reactive oxygen species (ROSs) for water disinfection. The BP-CN photocatalyst is composed of low-cost and earth-abundant materials and holds great promise in “green” photocatalytic disinfection applications.

In-situ homodispersely immobilization of Ag@AgCl on chloridized g-C3N4 nanosheets as an ultrastable plasmonic photocatalyst

Despite their impressive plasmonic photocatalytic activity, nanosized silver and silver halides always suffer from serious agglomeration and photocorrosion, thus are severely restricted in the practical wastewater restoration applications. The design and realization of plasmonic heterojunction nanostructures is an effective way to solve this stability problem, yet the ideal plasmonic catalyst dispersion and immobilization remains a great challenge. In this work, a highly immobilized Ag@AgCl/g-C3N4 plasmonic photocatalyst was developed through a rational in-situ implanting approach, in which the Ag can be homodispersely distributed and strongly coupled with prefixed Cl sites on g-C3N4 nanosheets (CNNS). The X-ray diffraction (XRD) pattern, X-ray photoelectron spectroscopy (XPS) spectra and element mapping images clearly proved the homodispersely distribution of nanosized Ag@AgCl on the CNNS. The optimal Ag@AgCl-3/CNNS plasmonic photocatalyst with a narrow band gap of 2.45 eV and large specific surface area of 52.9 m2/g performs well in model pharmaceutical wastewater bleaching reactions under visible light. More importantly, the Ag@AgCl-3/CNNS show good stability compared with the conventional inhomogeneously coupled AgCl/g-C3N4 control as verified by their ultralow silver leakage rate in water (0.00152 mg/g·d, accounts 6.9% that of the control) and a much lower corrosion current density (Icorr = 1.63 vs. 3.45 μA), recorded by Tafel slopes. The synergetic effect of surface plasmon resonance effect of nanosized Ag@AgCl with strong visible light harvesting ability and strong coupling between Ag@AgCl and exfoliated porous g-C3N4 nanosheets can support the fast separation of photogenerated electron–hole pairs, thus significantly improving the photocatalytic efficiency in the bleaching of antibiotic pollutants and bacteria. This work affords the great potential of the rational in-situ implanting design for high-performance and stable plasmonic photocatalysts.

Fullerene polymer film as a highly efficient photocatalyst for selective solar fuel production from CO2

ABSTRACTC60‐based polymeric systems have been constantly anticipated for sustainable solar energy conversion. Reported, herein is a C60 polymer film as visible light active photocatalyst for efficient and selective reduction of CO2 for the first time. The C60 polymer photocatalyst is synthesized via covalent coupling of C60 monomer units consisting of tetra substituted C60‐pyrene conjugates through spacer groups. The synthesized C60 polymer photocatalyst possesses an extended network of well‐defined repeating monomer units with good stability and visible light‐induced photocatalytic activity. The enhanced visible light harvesting ability of C60 polymer photocatalyst reasonably yields it with higher catalytic ability than its monomer unit. The C60 polymer film photocatalyst upon coupling with the biocatalyst carries out highly selective visible light driven reduction of CO2 to HCOOH (239.46 μmol). The tandem way of incorporating C60 into visible light active polymeric films for continuous use may be highly rewarding for their extended photocatalytic activity for solar fuel production from CO2. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48536.

Tailoring of crystalline structure of carbon nitride for superior photocatalytic hydrogen evolution

Light absorption and carrier transfer, are two sequential and complementary steps related to photocatalysis performance, whereas the collective integration of these two aspects into graphitic carbon nitride (g-C3N4) photocatalyst through polycondensation optimization have seldom been achieved. Herein, we report on tailoring the crystalline structure of g-C3N4 by avoiding the formation of incompletely reacted N-rich intermediates and selective breaking the hydrogen bonds between the layers of g-C3N4 simultaneously. The obtained layer plane ordered porous carbon nitride (LOP-CN) material shows efficient photocatalytic H2 generation performance. The highest H2 evolution rate achieved is 53.8 μmol under λ ≥ 400 nm light irradiation, which is 7.4 times higher than that of g-C3N4 prepared by convention thermal polycondensation. The substantially boosted photocatalytic activity is mainly ascribed to the efficient charge separation on long-range atomic order layer plane and the extended visible light harvesting ability. This work highlights the importance of crystalline structure tailoring in improving charge separation and light absorption of g-C3N4 photocatalyst for boosting its photocatalytic H2 evolution activity.

Efficient photoelectrochemical water-splitting over carbon membrane linked Au and TiO2 nanotube arrays film based on multiple carriers transport paths

Herein, a carbon membrane and Au nanoparticles were combined to improve the efficiency of photoelectrocatalytic water splitting over a TiO2 nanotube arrays film (TiO2 NTAF). Two different ternary nanostructures were constructed by hydrothermal and photochemical deposition processes. One was carbon membrane bridged Au nanoparticles and TiO2 nanotube arrays (Au/C/TiO2 NTAF), while the other was Au nanoparticles sandwiched between carbon membrane and TiO2 nanotube arrays (C/Au/TiO2 NTAF). The two structures exhibited enhanced visible light harvesting ability, but they showed distinctly different photoelectric properties. The unique microstructure of C/Au/TiO2 NTAF resulted in a much higher reduction of the electron cloud density of Au nanoparticles as carrier recombination centers, which were responsible for its poor photoelectrochemical performance. However, a champion photocurrent of Au/C/TiO2 NTAF was observed (0.984 mA cm−2), indicating superior ability of the photoelectrocatalytic water splitting. The great enhancement was attributed to multiple carriers transport paths, which can efficiently utilize the sensitization of the carbon membrane and the surface plasmon resonance effect of the Au nanoparticles.

Fabrication and characterization of Ag/BiOI/GO composites with enhanced photocatalytic activity

A ternary silver/bismuth oxyiodide/graphene oxide (Ag/BiOI/GO) composite photocatalyst was prepared with a facile chemical method; the BiOI modification was performed through noble metal surface sedimentation and nonmetal doping. The morphologies, chemical properties, and photocatalytic performances of the photocatalysts were characterized in detail using SEM, TEM, XRD, XPS, FT-IR, Raman spectroscopy, UV-Vis spectroscopy, EIS and PL. Compared with BiOI, Ag/BiOI, and GO/BiOI, the prepared Ag/BiOI/GO catalyst (doped with 2.0 wt% GO and 1.5 wt% Ag) exhibited the highest photocatalytic activity, with a RhB degradation rate of up to 99.12% within 120 min. The Ag/BiOI/GO catalyst was stable even after being recycled and reused. The photocatalytic mechanism could be that the coexistence of Ag and GO on the BiOI greatly promotes the visible light harvesting ability while inhibiting the recombination of photogenerated electron/hole pairs. This work provides novel insights into the development of new photocatalytic materials for organic compound removal.

Polymeric carbon nitride hybridized by CuInS2 quantum dots for photocatalytic hydrogen evolution

A p-n heterojunction photocatalyst for water splitting is synthesized by incorporating p-type CuInS2 quantum dots (QDs) into n-type polymeric carbon nitride (CN) by a self-assembly and calcination method. Benefiting from the enhanced electron-hole separation efficiency and improved visible light harvesting ability, the hydrogen evolution rate (HER) of the CuInS2/CN hybrid is two-folds higher than that of pristine CN. This work will open up new opportunities for the creation of highly-efficient photocatalysts for solar energy conversion.

Novel ultralong hollow hyperbranched Cu2–xSe with nanosheets hierarchical structure: Preparation, formation mechanism and properties

Cubic phase of novel hollow hyperbranched Cu2–xSe with nanosheets hierarchical structure was prepared on a Cu foil substrate by a facile solution route, using CuO nanosheets film as a precursor, and its formation mechanism was explored. The optical, gas sensing and superparamagnetic properties of the hollow hyperbranched Cu2–xSe were studied. The results show that the hollow hyperbranched Cu2–xSe microstructure could grow as long as 118 μm with diameters of 2–4 μm. Each hyperbranched Cu2–xSe contains four orthogonally located side branches and each side branch is composed of four orthogonal sub-branches which are assembled by numerous parallelly located nanosheets. The hollow hyperbranched Cu2–xSe microstructures were formed through the transformation reactions from CuO nanosheets to Cu2–xSe nanosheets, where the CuO nanosheets function as the sacrificing template, followed by multilevel oriented self-assembly. We found that the ultralong hollow hyperbranched Cu2–xSe microstructures possess extraordinary superparamagnetic property at room temperature. Besides, the Cu2–xSe product displays strong UV–visible light-harvesting ability and excellent gas sensing property to ammonia gas.

Nanocomposite Ag@AgCl/ZnO for efficient hydrogen generation through water splitting

We had successfully prepared the microwave assisted lotus shaped Ag@AgCl/ZnO nanocomposite (NC) of size 57.72 nm, in aqueous media at 90 °C for 7 min heating. The conventional single pot refluxing method was also used to prepare NCs with spherical shaped nanoparticles of size 59.12 nm at 90 °C heating for 3 h. X-ray diffraction data of the Ag@AgCl/ZnO NCs synthesized by the both methods, confirmed that the nanocomposite crystallized in three phases i.e. face-centered cubic (AgCl), cubic (nanosilver) and wurtzite hexagonal phase (ZnO). Energy dispersive X-rays corresponding to the electron microscopy analysis with their elemental mapping, envisioned the surface morphology and elemental composition i.e., 19% ZnO, 13.79% AgCl, 8.08% Zn and 26.19% Ag in the NC. The Ag@AgCl/ZnO NCs exhibited the visible light harvesting ability with band gap i.e. 3.02 and 2.96 eV with SURS selfsensitization of AgCl. Conventionally made sample and microwave assisted sample emits green and yellow-photoluminescence emissions, respectively. FTIR spectra at different stages of the formation of the nanocomposites, visualized the gradual changes in bonding positions of NCs. We utilized this molecular system as an efficient visible-light harvesting optical devices for water splitting. Conventionally and microwave assisted Ag@AgCl/ZnO samples, librated 6082.9 and 6782.32 μmol H2 h−1 g−1, optimum hydrogen in 8 h, respectively, through photocatalytic water splitting under AM 1.5G irradiation.

Three-dimensional plasmonic photoanode of Co3O4 nanosheets coated onto TiO2 nanorod arrays for visible-light-driven water splitting

In this work, we report for the first time a plasmonic photoanode by decorating Au nanoparticles (NPs) onto two-dimensional (2D) Co3O4 nanosheets (NSs)/one-dimensional (1D) TiO2 nanorod arrays (NRAs) (Au/Co3O4/TiO2-NRAs) for enhanced visible-light photoelectrochemical (PEC) water splitting. In this plasmonic photoanode, TiO2 NRAs act as an electron acceptor, plasmonic Au NPs and hierarchical Co3O4 NSs serve as visible-light harvesters. Light absorption shows that Au/Co3O4/TiO2-NRAs heterojunction architectures exhibit greatly improved ability to harvest visible light due to the surface plasmon resonance (SPR) absorption of Au NPs and visible light harvesting ability of Co3O4 NSs. Spectroscopic measurements demonstrate that a type II band alignment is formed between Co3O4 and TiO2. Benefiting from the SPR effect, type II band alignment and novel hierarchical architecture, plasmonic Au/Co3O4/TiO2-NRAs photoanode shows remarkably enhanced visible-light PEC water splitting activity compared with Co3O4/TiO2-NRAs and pristine TiO2-NRAs photoanodes. Photocurrent density achieved by plasmonic photoanode is 37 and 1.2 times higher than those of TiO2-NRAs and Co3O4/TiO2-NRAs photoanodes, respectively. This work provides a promising strategy to highly enhance visible-light PEC water splitting activity of wide band-gap semiconductor-based photoelectrode materials.

Plasmonic Au nanoparticles supported on both sides of TiO2 hollow spheres for maximising photocatalytic activity under visible light

A strategy of intensifying the visible light harvesting ability of anatase TiO2 hollow spheres (HSs) was developed, in which both sides of TiO2 HSs were utilised for stabilising Au nanoparticles (NPs) through the sacrificial templating method and convex surface-induced confinement. The composite structure of single Au NP yolk-TiO2 shell-Au NPs, denoted as Au@Au(TiO2, was rendered and confirmed by the transmission electron microscopy analysis. Au@Au(TiO2 showed enhanced photocatalytic activity in the degradation of methylene blue and phenol in aqueous phase under visible light surpassing that of other reference materials such as Au(TiO2 by 77% and Au@P25 by 52%, respectively, in phenol degradation.

The reinforced photocatalytic performance of binary-phased composites Bi-Bi12O17Cl2 fabricated by a facile chemical reduction protocol

Photocatalysis has been considered as an environmentally benign and sustainable technology for contaminants remediation and energy storage and the crucial issue is to design and fabricate catalysts with high visible-light sensitivity and photocatalytic performance. In this work, a series of binary-phased semi-metallic Bi decorated Bi12O17Cl2 composites (Bi-BOC) were constructed via a facile in-situ chemical reduction protocol using the NaBH4 as a reducing agent for the first time. X-ray diffraction patterns, X-ray photoelectron spectroscopy, and UV–vis diffuse reflection spectroscopy confirmed the real coexistence of both components that were closely contacted to form heterojunction domains in composites, as indicated by HRTEM observations. Under the visible light illumination, the as-achieved composites especially Bi-BOC-0.25 with the favorable phase composition, exerted efficient catalytic performance not only for degradation of both dye Rhodamine B and antibiotic tetracycline hydrochloride, but also for selective oxidation of benzyl alcohol. The reinforced photocatalytic capacity of these modified BOC series was mainly relevant to the effective separation of charge carriers by semimetal-semiconductor heterostructures, strengthened visible-light harvesting ability caused by the localized surface plasmon resonance effect of zero-valence Bi nanoparticles on surface, and good maintenance of original hierarchical morphology. In addition, active radicals entrapping experiments were carried out to deduce a preliminary photocatalysis mechanism.

Facile construction of flower-like bismuth oxybromide/bismuth oxide formate p-n heterojunctions with significantly enhanced photocatalytic performance under visible light

Visible-light harvesting ability and charge separation efficiency are two pivotal factors for the design and construction of photocatalysts with an efficient ability for degrading toxic pollutants. Herein, visible-light-driven (VLD) BiOBr/BiOCOOH p-n heterojunction photocatalysts were prepared via an in-situ anion-exchange route. Through controlling the addition of KBr, we synthesized a series of BiOBr/BiOCOOH p-n heterojunctions with a different BiOBr loading. During the process, BiOBr production and homogeneous deposition on BiOCOOH with close interfacial interactions were realized by employing BiOCOOH microspheres as the self-sacrificing template. Compared to bare BiOBr and BiOCOOH, such p-n heterojunctions displayed dramatically strengthened performance in decomposing the industrial dye (rhodamine B, RhB) and antibiotic (tetracycline chloride, TC) under the irradiation of visible light. Among them, BiOBr/BiOCOOH p-n heterojunction with a BiOBr/BiOCOOH theoretical molar ratio of 0.6/0.4 (0.6Br-Bi) achieved the highest performance. Moreover, 0.6Br-Bi showed a good durability, indicating BiOBr/BiOCOOH p-n heterojunction possessed an excellently stable photocatalytic activity. Such an efficient and stable photocatalytic performance was mainly due to the formation of p-n heterojunctions which can profoundly improve the visible-light absorption and significantly depress the recombination of charge carriers. Trapping experiments and ESR tests verified that superoxide free radicals (O2−) and photogenerated hole (h+) played a significant role in RhB degradation. This research affords a promising p-n heterojunction catalyst for wastewater treatment.