•A new visible-light photocatalyst was prepared from ZnFe2O4 and polyvinyl chloride.•The new photocatalyst was of core/shell structure ZnFe2O4/CPVC nanocomposites.•The new photocatalyst had much higher activity than ZnFe2O4 in Cr(VI) reduction.This communication reports the development of a new efficient visible-light-driven composite photocatalyst comprising ZnFe2O4 nanoparticles and conjugated polymer (CPVC) from the dehydrochlorination of polyvinyl chloride (PVC). ZnFe2O4/CPVC nanocomposites were synthesized via three main steps: (i) the synthesis of ZnFe2O4 nanoparticles by a sol-gel method; (ii) the adsorption of PVC in tetrahydrofuran solution by ZnFe2O4 nanoparticles to form ZnFe2O4/PVC nanocomposites; and (iii) the dehydrochlorination of PVC in the ZnFe2O4/PVC nanocomposites by heating at 150 °C for 2 h. X-ray diffraction, Fourier transform infrared spectroscopy and high-resolution transmission electron microscopy characterization revealed that the as-synthesized product was core/shell structured ZnFe2O4/CPVC nanocomposites. The photocatalytic results demonstrated that the ZnFe2O4/CPVC nanocomposites had much higher photocatalytic activity than ZnFe2O4 nanoparticles in the reduction of aqueous Cr(VI) under visible-light (λ>420 nm) irradiation. Thus, ZnFe2O4/CPVC nanocomposites are promising for use as a new efficient visible-light-driven photocatalyst.

•N-doped ThO2 was synthesized by a nitric acid-assisted one-step solvothermal method.•N-doped ThO2 exhibited obvious absorption of visible-light.•N-doped ThO2 had high visible-light photocatalytic activity in Cr(VI) reduction.•Highly toxic Cr(VI) was reduced to much less toxic Cr(III).•The ThO2 synthesized using ammonia had little visible-light photocatalytic activity.Nanostructure N-doped ThO2 (which was named as ThO2-HNO3) was synthesized by solvothermal treatment of Th(NO3)4·4H2O in the mixed solution of absolute ethanol (92.5 vol%) and nitric acid (7.5 vol%) at 180 °C for 20 h. ThO2-HNO3 exhibited significant visible-light absorption and high photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (wavelength > 420 nm) irradiation. By contrast, the commercial ThO2 and the ThO2 synthesized when ammonia replaced nitric acid exhibited only negligible visible-light photocatalytic activity. Thus, ThO2-HNO3 is a new alternative visible-light photocatalyst for treating Cr(VI)-polluted wastewaters.Download high-res image (85KB)Download full-size image

•A new visible-light photocatalyst was synthesized from SnS2 and polyvinyl alcohol.•The new catalyst was far more efficient than SnS2 in the treatment of aqueous Cr(VI).•The new catalyst showed superior optical and photoelectrochemical properties.•Mechanism for the new catalyst’s enhanced photocatalytic activity was elucidated.•The effects of catalyst dosage, pH and concentration of Cr(VI) solution were studied.This study focuses on the synthesis of a new high efficiency visible-light photocatalyst made of SnS2 and conjugated derivative (CPVA) from thermal dehydration of polyvinyl alcohol (PVA), and the evaluation of its performance in photocatalytic reduction of aqueous Cr(VI). SnS2/CPVA nanocomposites were synthesized via the procedures of (i) mixing of SnS2 nanocrystals and PVA in aqueous solution and evaporation of the aqueous solvent to generate SnS2/PVA nanocomposites, and (ii) thermal treatment of the SnS2/PVA nanocomposites for transforming their PVA into conjugated CPVA. The optimum conditions for synthesis of most efficient SnS2/CPVA nanocomposite were explored. The characterization by X-ray diffraction, Raman spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, high resolution transmission electron microscopy and elemental mapping indicated the formation of SnS2/CPVA nanocomposites. The photocatalytic experiments showed that SnS2/CPVA nanocomposite synthesized under the optimum conditions (SnS2/CPVA-1%-180 °C-2 h) had exceptionally higher photocatalytic activity than SnS2 nanocrystals, physical mixture of SnS2 nanocrystals and CPVA, SnS2/CPVC nanocomposite and TiO2/CPVA nanocomposite in the reduction of aqueous Cr(VI) under visible-light (wavelength > 420 nm) irradiation. The mechanism underlying the most enhanced photocatalytic activity of SnS2/CPVA-1%-180 °C-2 h was elucidated, based upon comparison between the optical, photoelectric and electrochemical impedance properties of SnS2 nanocrystals and different SnS2/CPVA nanocomposites. Furthermore, the effects of photocatalytic experiment parameters (including dosage of photocatalyst, and initial pH and concentration of Cr(VI) aqueous solution) on the Cr(VI) removal efficiency by SnS2/CPVA-1%-180 °C-2 h were also studied.Download high-res image (184KB)Download full-size image

•Scalable in air solid phase synthesis of pure SnS2 (F-SnS2) at 170 °C.•F-SnS2 has nanosheets-constructed porous flower-like hierarchical nanostructure.•F-SnS2 showed more adsorption and faster photocatalytic reduction of aqueous Cr(VI).•Reasons for the superior performance of F-SnS2 were proposed.•Effects of dosage of catalyst, pH and concentration of Cr(VI) solution were studied.Nanosheets-constructed porous flower-like hierarchical nanostructure SnS2 (which was labeled as F-SnS2) was synthesized by heating the mixture of SnCl2·2H2O and thiourea in air at 170 °C for 2 h, in combination with a subsequent washing with water. F-SnS2 exhibited much more adsorption and faster visible-light (wavelength >420 nm)-irradiated photocatalytic reduction of aqueous Cr(VI), as compared with SnS2 nanoparticles, nanoplates-assembled flowerlike hierarchical structure SnS2 synthesized by hydrothermal method, Fe, N and C tri-doped TiO2, and hydrothermally treated g-C3N4. The underlying reasons for the far superior performance of F-SnS2 were proposed, based on the comparison of the microstructure, specific surface area, optical, electrochemical impedance, photocurrent, surface charge, and Cr(VI) adsorption properties of F-SnS2 and SnS2 nanoparticles. Besides, the photocatalytic reusability and stability of F-SnS2, as well as the effects of photocatalytic testing parameters (including dosage of photocatalyst, initial pH and concentration of K2Cr2O7 aqueous solution) on the Cr(VI) removal efficiency by F-SnS2 were also studied. This work may advance our knowledge on the scalable low temperature solid phase synthesis of SnS2 nanomaterial, and contribute to the application of SnS2 in treating the Cr(VI)-polluted water.

•Porous nanostructure LaFeO3 was synthesized by gel-combustion method at 200 °C.•Lower calcining temperature resulted in enhanced photoabsorption of LaFeO3.•Lower calcining temperature resulted in higher photocatalytic activity of LaFeO3.•LaFeO3 was studied for the first time in photocatalytic treatment of Cr(VI).LaFeO3 was synthesized via a simple gel-combustion method at the calcination temperatures of 200–400 °C. The X-ray diffraction characterization indicated that the products synthesized at 200–400 °C were all pure perovskite phase LaFeO3. The scanning electron microscopy images revealed that the LaFeO3 synthesized at 200 °C had a porous nanostructure, but became a solid nanostructure at 400 °C. The nitrogen adsorption measurements suggested that the specific surface area of LaFeO3 increased with the lowering of the calcination temperature. The UV–vis diffuse reflection spectra showed that the LaFeO3 synthesized at 200 °C exhibited the strongest absorption of visible-light. The photocatalytic experiments demonstrated that as the calcination temperature was lowered, the resultant LaFeO3 exhibited obviously enhanced photocatalytic activity in reduction of Cr(VI) in aqueous solution under visible-light (wavelength longer than 420 nm) irradiation. This work can enrich our knowledge on the synthesis and photoabsorption properties of porous nanostructure LaFeO3, and contribute to the application of LaFeO3 nanomaterials in treating the wastewaters contaminated by highly toxic and intractable Cr(VI).

•N-modified Nb2O5 was prepared by one-step solvothermal method using HNO3 as N source.•Strong and wide absorption of visible light.•High photocatalytic activity in the reduction of aqueous Cr6+ under visible light.•Nb2O5 prepared using NH3·H2O had no visible light-driven photocatalytic activity.This letter reports the preparation of visible light-driven N-modified Nb2O5 photocatalyst by an alternative one-step solvothermal route, which employs nitric acid as the nitrogen source. N-modified Nb2O5 nanoparticles (which were abbreviated as Nb2O5–HNO3) were prepared directly through the solvothermal reactions of NbCl5, nitric acid (14.36–15.16 mol/L) and absolute ethanol at 200 °C for 15 h. The composition, structure and photoabsorption feature of Nb2O5–HNO3 were characterized by X-ray photoelectron spectroscopy, transmission electron microscopy, N2 adsorption/desorption isotherms and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of Nb2O5–HNO3 was examined in the reduction of aqueous Cr(VI) under visible light (λ>420 nm) irradiation, and compared with that of Nb2O5–NH3 (which denoted the sample prepared when 13.32–14.44 mol/L ammonia water replaced nitric acid). It was observed that Nb2O5–HNO3 displayed distinct absorption of visible light and high photocatalytic activity in the reduction of aqueous Cr(VI) under visible light (λ>420 nm) irradiation, whereas Nb2O5–NH3 exhibited no visible light-absorbing ability and no visible light-driven photocatalytic activity. This work suggests that nitric acid is an alternative nitrogen source for one-step solvothermal preparation of visible light-driven N-modified Nb2O5 photocatalyst.

•g-C3N4 was treated in dilute NaOH aqueous solution for better performance.•Treated g-C3N4 had much higher photocatalytic activity in Cr6+ reduction.•Structure and other properties of treated g-C3N4 were characterized.•Reasons for the enhanced photocatalytic activity of treated g-C3N4 were proposed.A simple, effective and environmental-friendly method was adopted for enhancing the photocatalytic activity of g-C3N4 (which was synthesized by thermal condensation of melamine) in the reduction of aqueous Cr6+ under visible-light irradiation. The enhancement was achieved via treatment of g-C3N4 in 0.2 mol/L NaOH aqueous solution at 80 °C for 6 h. The photocatalytic experiments demonstrated that the treated g-C3N4 exhibited much higher photocatalytic activity than pristine g-C3N4 in the reduction of aqueous Cr6+ under visible-light (λ>420 nm) irradiation (for example, the reduced ratios of Cr6+ in the presence of the treated g-C3N4 and pristine g-C3N4 were 100% and 29.4%, respectively, when irradiated for 120 min). Based on the characterization results of the structures and other physiochemical properties of the treated g-C3N4 and pristine g-C3N4 by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption/desorption isotherms, photocurrent measurement and electrochemical impedance spectroscopy, the possible reasons responsible for the enhanced photocatalytic activity of the treated g-C3N4 were proposed.

•Mixing and heating synthesis of partially conjugated PVC-modified TiO2 nanoparticles.•Strong absorption of visible-light.•High visible-light-driven photocatalytic activity in the reduction of aqueous Cr(VI).Partially conjugated polyvinyl chloride (CPVC)-modified TiO2 nanoparticles were synthesized by heating the composite of polyvinyl chloride and TiO2 nanoparticles in air at 150 °C for 1 h (the optimal heating duration among the investigated 0.5 h, 1 h, 2 h, 3 h and 4 h to obtain the most efficient CPVC/TiO2 composite). The characterization results from X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy and high resolution transmission electron microscopy confirmed the formation of TiO2 nanoparticles modified with CPVC. The UV–vis diffuse reflectance spectra indicated that the as-synthesized CPVC-modified TiO2 nanoparticles had remarkable visible-light-absorbing ability. The photocatalytic experiments demonstrated that the as-synthesized CPVC-modified TiO2 nanoparticles exhibited high photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ>420 nm) irradiation, whereas sole CPVC and TiO2 nanoparticles exhibited no photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ>420 nm) irradiation.

•Acid-soaking treatment can improve the photocatalytic activity of g-C3N4.•5 mol/L HNO3 treatment can remove the Cr(III) deposited on the used g-C3N4.•5 mol/L HNO3-treated g-C3N4 exhibited higher photocatalytic efficiencies in reuses.An alternative simple, economical and efficient acid-soaking method was proposed to improve the activity of g-C3N4 for photocatalytic reduction of aqueous Cr(VI) in this work. The improvement was achieved simply by soaking g-C3N4 (which was obtained by heating melamine in air at 550 °C for 4 h) in 5 mol/L HNO3 or HCl aqueous solution for 2 h (the HNO3 and HCl-treated samples were denoted as g-C3N4HNO3 and g-C3N4HCl, respectively). The compositions, structures, Brunner–Emmet–Teller (BET) specific surface areas, Zeta potentials and optical properties of g-C3N4, g-C3N4HNO3 and g-C3N4HCl were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, N2 adsorption/desorption isotherms, Zeta potential analyzer and UV–vis diffuse reflectance spectroscopy. The photocatalytic properties of g-C3N4, g-C3N4HNO3 and g-C3N4HCl were tested in the reduction of aqueous Cr(VI) under visible-light (λ > 420 nm) irradiation. It was observed that both g-C3N4HNO3 and g-C3N4HCl exhibited higher photocatalytic activity than g-C3N4. The higher photocatalytic activities of acid-treated samples may be attributed to their larger BET specific surface areas, positive surface charges and larger adsorption capacities for Cr(VI). Furthermore, the soaking treatment with 5 mol/L HNO3 aqueous solution can not only remove the Cr(III) species deposited on the surface of g-C3N4HNO3 after use in photocatalytic reduction of aqueous Cr(VI), but also enhance the photocatalytic efficiency of g-C3N4HNO3 in reuse.

•Nanocrystalline N-modified CeO2 was prepared by a HNO3-involved solvothermal method.•Strong and wide absorption of visible-light.•High photocatalytic activity in the reduction of aqueous Cr6+ under visible-light.This work reports an alternative preparation and evaluation of nanocrystalline N-modified CeO2 as a visible-light-active photocatalyst. Nanocrystalline N-modified CeO2 (which was abbreviated as CeO2–HNO3) was synthesized directly via the solvothermal reactions of Ce(NO3)3·6H2O, concentrated (65–68 mass%) HNO3 and toluene at 180 °C for 24 h. The composition, structure and optical property of CeO2–HNO3 were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of CeO2–HNO3 was tested in the reduction of aqueous Cr6+ under visible-light (λ>420 nm) irradiation, and compared with that of CeO2–NH3 (which denoted the product prepared when 25-28 mass% NH3·H2O replaced 65–68 mass% HNO3). It was observed that CeO2–HNO3 exhibited much higher photocatalytic activity than CeO2–NH3 in the reduction of aqueous Cr6+ under visible-light (λ>420 nm) irradiation. CeO2–HNO3 may be a new promising visible-light-active photocatalyst in efficient utilization of solar energy for treating Cr6+ wastewater.

•SnS2/SnO2 nanocomposite prepared by thermal oxidation of SnS2 nanoparticles in air.•Higher photocatalytic activity than SnS2, SnO2 and physical mixture of SnS2 and SnO2.•Good reusability in photocatalytic reduction of aqueous Cr(VI).•Coexistence of phenol and RhB enhanced photocatalytic reduction of Cr(VI).An alternative in situ chemical method, which was based on thermal oxidation of SnS2 nanoparticles in air at 300 °C for 3 h, was proposed for the preparation of SnS2/SnO2 nanocomposite (SnS2/SnO2-TO). The photocatalytic properties of SnS2/SnO2-TO were tested by the reduction of aqueous Cr(VI) under visible-light (λ > 420 nm) irradiation, and compared with those of SnS2 nanoparticles, SnO2 nanoparticles and SnS2/SnO2-PM (which denotes the physically mixed SnS2/SnO2 nanocomposite with the same composition as SnS2/SnO2-TO). Besides, the effects of the coexistence of some organic compounds (e.g., phenol, rhodamine B (RhB) and methyl orange (MO)) on SnS2/SnO2-TO-mediated photocatalytic reduction of aqueous Cr(VI) were also studied. It was observed that (i) SnS2/SnO2-TO not only displayed higher visible-light-activated photocatalytic activity than SnS2, SnO2 and SnS2/SnO2-PM, but also displayed good reusability in the reduction of aqueous Cr(VI); and (ii) the coexistence of phenol and RhB enhanced the photocatalytic reduction of Cr(VI), whereas the coexistence of MO retarded the photocatalytic reduction of Cr(VI) over SnS2/SnO2-TO. The reasons accounting for the photocatalytic results were also discussed.

•Nonmetals-modified SnO2 was synthesized by a HNO3-involved solvothermal method.•High specific surface area and excellent visible-light-absorbing ability.•High photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light.•Photocatalyst dosage and Cr(VI) concentration affect the reduction rate of Cr(VI).This work took the initiative to conduct the synthesis and evaluation of visible-light-active nonmetals (N, C and Cl)-modified SnO2 nanoparticles for photocatalytic reduction of aqueous Cr(VI). Using inexpensive SnCl4⋅5H2O, absolute ethanol and concentrated (65–68 mass%) nitric acid as the starting materials, a one-step low temperature (180 °C) solvothermal method was developed for the synthesis of nonmetals (N, C and Cl)-modified SnO2 nanoparticles (which was abbreviated as SnO2–HNO3). The composition, structure, BET specific surface area and optical property of SnO2–HNO3 were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, N2 adsorption and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of SnO2–HNO3 was tested in the reduction of aqueous Cr(VI) under visible-light (λ > 420 nm) irradiation, and compared with that of SnO2–NH3 (which denoted the product synthesized when 65–68 mass% HNO3 was replaced by 25–28 mass% NH3⋅H2O). It was observed that SnO2–HNO3 exhibited high photocatalytic activity, whereas SnO2–NH3 exhibited no photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ > 420 nm) irradiation. Besides, the dosage of SnO2–HNO3 and the initial concentration of Cr(VI) aqueous solution had great effects on the photocatalytic reduction rate of Cr(VI). This work suggests that SnO2–HNO3 is a new promising visible-light-activated photocatalyst in efficient utilization of solar energy for treating Cr(VI) wastewater.

•I-Cu2WS4 submicron crystallites were prepared by a hydrothermal method.•They display a direct bandgap of about 2.15 eV.•They have high photocatalytic activity in reducing aqueous Cr6+ under visible-light.An inexpensive and less pollutive hydrothermal method, which was based on the autoclave-sealed reactions of CuCl, Na2WO4·2H2O and thioacetamide in mixed solution of equal volume of water and ethanol at 190 °C for 72 h, was employed to synthesize Cu2WS4. X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and N2 adsorption–desorption isotherms indicated that the as-synthesized product was body-centered tetragonal structure Cu2WS4 (I-Cu2WS4) submicron crystallites with a BET specific surface area of 2.199 m2/g. UV–vis diffuse reflectance spectrum suggested that the as-synthesized I-Cu2WS4 submicron crystallites had a direct bandgap of about 2.15 eV. Besides, the as-synthesized I-Cu2WS4 submicron crystallites exhibited considerably high photocatalytic activity in the reduction of aqueous Cr(VI) under visible-light (λ>420 nm) irradiation.

•SnIn4S8/TiO2 nanocomposite was prepared by a one-step in situ solvothermal method.•Much higher photocatalytic activity than SnIn4S8 and TiO2 in reducing aqueous Cr(VI).•Initiative study of SnIn4S8/TiO2 composite photocatalyst.A one-step in situ solvothermal method was proposed for the synthesis of SnIn4S8/TiO2 nanocomposite with 6.5 mol% SnIn4S8, using SnCl4·5H2O, InCl3·4H2O, thiourea, tetrabutyl titanate and absolute ethanol as the source materials. The structure, composition, BET specific surface area and optical property of the as-synthesized SnIn4S8/TiO2 nanocomposite were characterized by powder X-ray diffraction, energy dispersive X-ray spectroscopy, field emission scanning electron microscopy, N2 adsorption and UV–vis diffuse reflectance spectra. The photocatalytic activity of the as-synthesized SnIn4S8/TiO2 nanocomposite was tested in the reduction of aqueous Cr(VI) under visible-light (λ>420 nm) irradiation, and compared with those of nanostructured SnIn4S8 and TiO2. The photocatalytic results demonstrated that the as-synthesized SnIn4S8/TiO2 nanocomposite exhibited much higher visible-light-activated photocatalytic activity than SnIn4S8 and TiO2 nanoparticles. The reasons accounting for the photocatalytic results were also discussed.

•SnS2/WO3 nanocomposite was synthesized by an in situ hydrothermal method.•Higher photocatalytic activity than SnS2 and WO3 in the reduction of aqueous Cr6+.•This work took the initiative to study the properties of SnS2/WO3 nanocomposite.SnS2/WO3 nanocomposite was synthesized via hydrothermal treatment of tin(IV) chloride pentahydrate, thioacetamide and WO3 nanoplates in deionized water at 160 °C for 6 h. The structure, composition, BET specific surface area and optical property of the as-synthesized SnS2/WO3 nanocomposite were characterized by powder X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy, N2 adsorption and UV–vis diffuse reflectance spectra. The photocatalytic activity of the as-synthesized SnS2/WO3 nanocomposite was tested in the reduction of aqueous Cr6+ under visible-light (λ>420 nm) irradiation, and compared with those of SnS2 nanoparticles and WO3 nanoplates. It was observed that the as-synthesized SnS2/WO3 nanocomposite exhibited higher visible-light-activated photocatalytic activity than SnS2 nanoparticles and WO3 nanoplates. The reasons accounting for the photocatalytic results were also discussed.

ZnO2 hollow nanospheres and nanotubes were synthesized via hydrothermal treatment of ZnO submicron-sized powder in 20 vol.% H2O2 aqueous solution at 120 °C for 6 h, and ZnO with similar hollow nanostructures could be obtained by thermal decomposition of the hydrothermally-synthesized ZnO2 hollow nanospheres and nanotubes in air at 200 °C for 6 h. The possible formation mechanisms of the ZnO2 and ZnO hollow nanostructures were proposed. The present work pointed out a simple, cost-effective and green way of converting bulk ZnO powder into hollow-nanostructured ZnO2 and ZnO powders. The as-synthesized hollow-nanostructured ZnO2 and ZnO powders have promising uses as catalysts, adsorbents and light weight fillers, etc.Highlights► Green synthesis of hollow-nanostructured ZnO2 and ZnO is achieved. ► Possible formation mechanisms of the products are proposed. ► A promising way of converting bulky ZnO into hollow-nanostructured ZnO.

A simple and cost-effective route was developed for the low temperature (700 °C) synthesis of K2Ti6O13 powder, using low-melting-point KNO3 and high-reactive-activity P25 TiO2 nanocrystals as the reactants. The characterization results from X-ray diffraction and field emission scanning electron microscopy revealed the successful preparation of monoclinic phase K2Ti6O13 crystallites with a rodlike morphology. UV–vis diffuse reflectance spectrum disclosed that the as-synthesized K2Ti6O13 had a direct optical band gap of about 3.47 eV. Besides, the as-synthesized K2Ti6O13 displayed strong and wide visible light emission in the wavelength range of about 400–700 nm upon laser excitation at 325 nm at room temperature, enabling its use as a promising blue light-emitting material.Highlights►Pure K2Ti6O13 was synthesized by a simple and cost-effective method at 700 °C. ►The source materials are low-melting-point KNO3 and high-reactive-activity P25 TiO2. ►The optical properties of the as-synthesized K2Ti6O13 were studied.

SnS2/SnO2 nanocomposites with tunable SnO2 contents were prepared via in situ hydrothermal oxidation of SnS2 nanoparticles in 0.375–4.5 mass% H2O2 aqueous solutions at 180 °C for 0–12 h. The structure, composition and optical properties of the as-prepared SnS2/SnO2 nanocomposites were characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, Brunauer–Emmett–Teller (BET) surface area analysis, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectra. Furthermore, their photocatalytic properties were tested for the degradation of methyl orange in water under visible light (λ > 420 nm) irradiation. It was found that the as-prepared SnS2/SnO2 nanocomposites with suitable SnO2 content not only demonstrated superior photocatalytic activity to both SnS2 nanoparticles and physically mixed SnS2/SnO2 composite nanoparticles, but also had remarkable photocatalytic stability. The tight attachment of SnO2 nanoparticles to SnS2 nanoparticles, which can facilitate interfacial electron transfer and reduce the self-agglomeration of two components, was considered to play an important role in achieving the high photocatalytic performances exhibited by the as-prepared SnS2/SnO2 nanocomposites.Keywords: in situ oxidation synthesis; nanocomposites; photocatalysis; stability; tin oxide; tin sulfide

SnS2 nanocrystals with adjustable sizes were synthesized via a hydrothermal method from the aqueous solution of common and inexpensive SnCl4·5H2O, thioacetamide and citric acid, simply by varying the reaction temperature and reaction time. The structures, Brunauer–Emmett–Teller (BET) specific surface areas and optical properties of the resultant SnS2 nanocrystals were characterized by X-ray diffraction, transmission electron microscopy, N2 adsorption/desorption isotherms, and UV–vis diffuse reflectance spectra. Besides, their photocatalytic properties were tested for the reduction of aqueous Cr(VI) under visible light (λ > 420 nm) irradiation. It was found that the photocatalytic activities of SnS2 nanocrystals in aqueous suspension depended on their synthesis conditions. The product synthesized under suitable hydrothermal conditions (for example, at 150 °C for 12 h) not only showed high visible light-driven photocatalytic activity in the reduction of aqueous Cr(VI), but also showed good photocatalytic stability. Our photocatalytic results suggested that SnS2 nanocrystals are a promising photocatalyst in the efficient utilization of solar energy for the treatment of Cr(VI)-containing wastewater.

A simple hydrothermal method was developed for the size-controlled synthesis of SnS2 nanoparticles, using common and inexpensive SnCl4·5H2O and thioacetamide as the reactants and 5 vol.% acetic acid aqueous solution as the solvent. The structure, composition and optical property of the obtained products were characterized by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Brumauer–Emmett–Teller (BET) surface area analysis and UV–vis diffuse reflectance spectra, and their possible formation mechanism was proposed. Besides, their photocatalytic properties were tested by degrading methyl orange in distilled water (20 mg/l) under visible light (λ > 420 nm) irradiation. It was found that SnS2 nanoparticles synthesized under the appropriate hydrothermal conditions not only exhibited high visible light-driven photocatalytic activity, but also had good photocatalytic stability.Highlights► Size-tunable synthesis of SnS2 nanoparticles is achieved by a hydrothermal method. ► The possible formation mechanism of size-tunable SnS2 nanoparticles is proposed. ► All products show higher activities than “200-0 SnS2”, flowerlike CdS and P25 TiO2. ► The product with the highest activity also had good photocatalytic stability.

Choosing low-melting-point Ca(NO3)2·4H2O and high-reactive-activity TiO2 nanocrystals as the raw materials, a simple and cost-effective route was developed for the synthesis of CaTiO3 nanoparticles at 600 °C, which is much lower than that (about 1350 °C) used in the conventional solid state reaction methods. X-ray diffraction, energy dispersive X-ray spectroscopy and field emission scanning electron microscopy revealed the formation of orthorhombic phase CaTiO3 nanoparticles with oxygen-deficiency at the surface. UV–vis absorption spectrum of the as-obtained CaTiO3 nanoparticles displayed an absorption peak centered at around 325 nm (3.8 eV), together with a tail at lower energy side. Room temperature photoluminescence spectrum of the as-obtained CaTiO3 nanoparticles upon laser excitation at 325 nm demonstrated a strong and broad visible light emission ranging from about 527 to 568 nm, which may be originated from the surface states and defect levels.

SnO2/SnS2 nanocomposite with a heterojunction structure (that is, SnO2 nanoparticles-decorated SnS2 nanoplates) was synthesized via the hydrothermal reaction between SnO2 nanoparticles and thioacetamide in 5 vol.% acetic acid aqueous solution at 150 °C for 3 h, and characterized by X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy and UV–vis diffuse reflectance spectra. The photocatalytic activity of the hydrothermally synthesized SnO2/SnS2 nanocomposite was tested by degrading methyl orange in distilled water under visible light (λ > 420 nm) irradiation. It was found that the hydrothermally synthesized SnO2/SnS2 nanocomposite exhibited superior photocatalytic activity to SnO2 nanoparticles, SnS2 nanoplates and physically mixed SnO2/SnS2 nanocomposite. The heterojunction structure of the hydrothermally synthesized SnO2/SnS2 nanocomposite, which can facilitate interfacial electron transfer and reduce the self-agglomeration of two components, was considered to play an important role in achieving its higher photocatalytic activity.Highlights► SnO2/SnS2 nanocomposite with a heterojunction structure (that is, SnO2 nanoparticles-decorated SnS2 nanoplates) was synthesized via a hydrothermal method. ► It exhibited higher visible light-driven photocatalytic activity than SnO2 nanoparticles, SnS2 nanoplates and physically mixed SnO2/SnS2 nanocomposite. ► The photocatalytic results were rationally explained.

A green hydrothermal method was proposed for the controllable synthesis of ZnO2 nanocrystals and ZnO nanorods, using the common and cost-effective 2ZnCO3·3Zn(OH)2 powder and 30 mass% H2O2 aqueous solution as the raw materials. The characterization results from X-ray diffraction, high resolution transmission electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy indicated that the products synthesized at 100–120 °C for 6 h or at 170 °C for 0 h were cubic phase ZnO2 nanocrystals; while those synthesized at 170 °C for 3–6 h were hexagonal phase ZnO nanorods. The UV–vis absorption spectra showed that the as-synthesized ZnO2 nanocrystals and ZnO nanorods had optical band gaps of about 4.1 and 3.3 eV, respectively.

Two routes have been proposed for the synthesis of In2O3 powders from InCl3•4H2O and thiourea. One route involved a two-step procedure (that is, firstly, In2S3 clusters constructed with mainly nanoflakes were synthesized by heating the mixture of InCl3•4H2O and thiourea in air from room temperature to 200 °C, coupled with a subsequent washing treatment; secondly, In2O3 was obtained by calcining the In2S3 clusters in air at 600 °C for 6 h), and the other route was a one-step procedure (that is, In2O3 was synthesized directly by calcining the mixture of InCl3•4H2O and thiourea in air at 600 °C for 6 h). The resultant products were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy, scanning electronic microscope and room temperature photoluminescence (RT-PL) spectra. It was observed that the In2O3 nanocrystals obtained via the two-step procedure exhibited PL peaks at about 453 and 471 nm, corresponding to the defeat-related emission; while the In2O3 submicron polyhedral crystals obtained via the one-step procedure and In2O3 pyramids obtained by calcining the only InCl3•4H2O in air at 600 °C for 6 h displayed a PL band centered at around 338 nm, corresponding to the band edge emission.

An eutectic NaCl–KCl molten salts method has been developed for the synthesis of SrTiO3 submicron crystallites and nanocrystals from SrO2 and two kinds (submicron and nano-sized) of TiO2 powders at 700 °C, which was much lower than that (generally > 1000 °C) of the conventional solid state reactions. The characterization results from X-ray diffraction and X-ray photoelectron spectroscopy revealed that the obtained products were pure perovskite phase SrTiO3 without any contamination of Na, K, and Cl ions. The scanning electronic microscopy and transmission electron microscopy images disclosed that the starting TiO2 played an important role in the morphology and size of the obtained SrTiO3: while the product derived from TiO2 submicron crystallites comprised faceted submicron crystallites of about 95–184 nm, that derived from TiO2 nanocrystals comprised quadrate nanocrystals of about 20–61 nm. Besides, based on the experiments without the molten NaCl–KCl eutectic, at different temperatures and times, and using different kinds of TiO2, the possible formation mechanism of SrTiO3 submicron crystallites and nanocrystals was proposed.

A green hydrothermal method has been developed for the synthesis of CdO2 nanoparticles from Cd(OH)2 powder and 6 vol.% H2O2 aqueous solution at 80–150 °C. The characterization results from X-ray diffraction, transmission electron microscopy, and thermal gravimetric and differential scanning calorimetry analysis disclosed that the resultant products were pure cubic phase CdO2 nanoparticles with the sizes in the range of about 11–13 nm. The UV–vis absorption spectra revealed that the as-synthesized CdO2 nanoparticles had similar optical band gaps of about 3.85 eV. The Raman spectra of the as-synthesized CdO2 nanoparticles displayed two obvious peaks at about 348 and 830/833 cm–1, a characteristic of pyrite-type IIB-peroxides.

Orthorhombic phase MoO3 nanoplates were synthesized directly by thermolysis of an air-stable metallorganic molecular precursor (molybdenum diethyldithiocarbamate oxide: Mo((C2H5)2NCS2)2O2, which was prepared simply through the precipitation reaction of ammonium peramolybdate and sodium diethyldithiocarbamate in distilled water under the ambient condition) in air at 350–400 °C for 5 h. The control experiments with ammonium peramolybdate as precursor could only obtain mostly irregular microcrystallites, indicating that the metallorganic molecular precursor, Mo((C2H5)2NCS2)2O2 played an important role in the successful synthesis of MoO3 nanoplates.

A molten salt method to synthesize SnS2 nanoplates, in a melt of tin dichloride and thiourea in air at 250–280 °C for 0–5 h, coupled with a subsequent washing treatment using distilled water, is demonstrated. The X-ray diffraction, Raman spectra, and field emission scanning electron microscope images disclosed that all the obtained products were phase pure hexagonal SnS2 nanoplates, of 20–70 nm thickness.

Without the assistance of any template and surfactant, In2S3 microspheres constructed with nanoflakes or nanoparticles were controllably synthesized via the hydrothermal reaction of InCl3·4H2O and Na2S2O3·5H2O in 6.25 vol.% acetic acid aqueous solution (pH = 3) at 150–180 °C for 6–24 h. The nanostructured In2S3 can be completely transformed into In2O3 when subjected to calcination in air at 600–700 °C for 5 h. The In2O3 produced at 600 °C consisted of microspheres built up with the nanoparticles of 20–30 nm in diameter. X-ray diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, field emission scanning electronic microscope, Raman and photoluminescence spectra have been used to characterize the structures, compositions and optical properties of the obtained products.

Cubic phase ZnS nanoparticles of several nanometers were synthesized directly via the liquid–solid reaction between zinc acetate and thiourea in air at 190 °C for 3 h. The structure, composition and optical property of the resultant product were characterized by means of X-ray powder diffraction (XRD), field emission scanning electron microscope (FESEM), energy dispersive X-ray spectrum (EDX), Raman and UV–vis absorption spectra. The proposed method has also been successfully extended to synthesize MnS, CuS, CdS, PbS nanoparticles, etc., and may serve as a general kind of simple, mild and cheap way to synthesize semiconducting metal sulfide nanomaterials on a large scale.

Zincblende structure cuprous bromide (γ-CuBr) nanocrystals were synthesized via a green hydrothermal method, which was based on the reactions of CuSO4·5H2O, KBr and d-glucose in distilled water in an autoclave at 100 °C for 12–24 h. The structure, composition and optical properties of the resultant products were characterized by means of X-ray powder diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis absorption and room temperature photoluminescence (RTPL) spectra. A possible reduction–precipitation mechanism was also proposed for the formation of CuBr in the present system.

SnS2 nanoplates were synthesized via the liquid–solid phase reactions of tin (Sn), sulfur (S) and ammonium chloride (NH4Cl) powders in air at 250 °C, combined with a subsequent washing treatment using distilled water. The phase, purity, morphology and size of the obtained products were characterized by powder X-ray diffraction (XRD), Raman, energy dispersive X-ray (EDX) spectra, and field emission scanning electron microscope (FESEM). The effects of additive NH4Cl on the phases of the resultant products were investigated, and the experimental results revealed that the additive NH4Cl played important roles in the synthesis of pure SnS2 under the current mild conditions.

GaOOH nanorods were synthesized by a green hydrothermal method at 200 °C using nanocrystalline Ga2O3 powders and distilled water as the starting materials, and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and thermogravimetric and differential scanning calorimetry (TG-DSC) analysis.

Ternary II–VI semiconductors have many excellent physical and chemical properties, and can be used in multiple technical fields. But their previous solid state synthesis methods usually need high reaction temperatures and rigorous conditions (e.g., in vacuum or under the protection of inert gases). In this letter, we report a novel solid state synthesis of hexagonal Cd1 − xZnxS (x = 0–1) nanoparticles in air from a class of solid air-stable single-source molecular precursors (cadmium zinc bis(N,N-diethyldithiocarbamate, Cd1 − xZnx-(DDTC)2) by two facile steps: firstly, Cd1 − xZnx-(DDTC)2 (x = 0–1) were prepared directly through the precipitation reactions of stoichiometric cadmium sulfate, zinc acetate and sodium diethyldithiocarbamate in distilled water under the ambient condition (8 °C, 1 atmospheric pressure); secondly, hexagonal Cd1 − xZnxS (x = 0–1) nanoparticles were produced simply via thermolysis of the single-source precursors in air at 300 °C for 3 h. The proposed method may serve as a kind of simple, mild and cheap way to synthesize nanomaterials of many ternary metal sulfide semiconductors, which have promising applications in the photocatalysis and optoelectronic devices.

CuCl, a wide bandgap (Eg = 3.395 eV at 4 K) I–VII semiconductor with excitonic binding energies of about 190 meV, can be used in the manufacture of electrooptic modulators, optical filters, solid-state batteries, catalyst, adsorbent, air purifying agents, blue-UV light-emitting devices, etc. Although many methods have already been developed for synthesizing CuCl powders with different characteristics so far, all of them either need complicated equipment and high reaction temperatures, or utilize toxic reactants and organic solvent, or produce much pollutive byproducts. In this paper, we report a green hydrothermal way to prepare nanocrystalline CuCl powders, simply by using the reaction of CuCl2 and alpha-d-glucose in distilled water in an autoclave at 120 °C for 24 h. The obtained CuCl nanocrystals were characterized by X-ray powder diffraction (XRD), scanning electron microscope (SEM) and X-ray photoelectron spectroscopy (XPS), and their possible formation mechanism was also proposed.

Pure submicrometer-sized copper and silver crystallites have been directly synthesized via solvothermal treatment of CuCl2·2H2O or AgNO3 in ethylenediamine (EDA) at 80–180 °C for 15–20 h, and characterized by means of X-ray powder diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and transmission electron microscopy. It was suggested that the formation of copper and silver crystallites in this solvothermal system be through a typical complexation–reduction process, in which EDA serves not only as a reducing reagent, but also as a complexing solvent.CuCl2·2H2O+xEDA→[Cu(EDA)x]2+⟶solvothermalCu,AgNO3+EDA→[Ag(EDA)]+⟶solvothermalAg.

Without the use of any extra surfactant, template or other additive, shape-controlled synthesis of sphere-, urchin- and tube-like CuS nanocrystallites has been realized just via hydrothermal treatment of different amounts of CuSO4·5H2O and equimolar Na2S2O3·5H2O in water at 150 °C for 12 h. The possible mechanism for the formation of the various nanostructures of CuS in this system was discussed.

•A new visible light photocatalyst was developed from SnS2 and polyvinyl chloride.•The new photocatalyst exhibited much higher activity than SnS2 in Cr(VI) reduction.•The new photocatalyst demonstrated good photocatalytic stability and reusability.•A photocatalytic mechanism was proposed.•Reasons for the new catalyst’s improved photocatalytic efficiency were elucidated.This work reports the development of a new efficient visible-light-driven composite photocatalyst comprising SnS2 nanoflakes and conjugated polymer (CPVC) from the dehydrochlorination of polyvinyl chloride (PVC). The optimum synthesis conditions were explored to obtain the most efficient SnS2/CPVC composite photocatalyst. The formation of SnS2/CPVC nanocomposites was confirmed by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, high-resolution transmission electron microscopy, and elemental mapping characterization. The photocatalytic tests demonstrated that SnS2/CPVC nanocomposites exhibited not only far higher visible-light-driven photocatalytic activity than SnS2 nanoflakes, but also good photocatalytic stability and reusability in the reduction of aqueous Cr(VI) under visible-light (λ > 420 nm) irradiation. The mechanism underlying the improved photocatalytic efficiency of SnS2/CPVC nanocomposites was elucidated, based on comparison between the optical, photoelectric, and electrochemical properties of SnS2/CPVC nanocomposites and SnS2 nanoflakes, as well as the matched electronic band structures between SnS2 and CPVC.Download high-res image (138KB)Download full-size image

A novel method based on heating the mixture of SnCl2·2H2O and excess S powders in air at 200–240 °C for 0–10 h (t = 0 h, that is, the heating of the reactants was stopped immediately once temperature reached the designed degree), coupled with a subsequent washing treatment, was proposed for the synthesis of SnS2 nanoflakes. X-ray diffraction, transmission electron microscopy, selected area electron diffraction and Raman spectra revealed the formation of bulk-pure hexagonal phase SnS2 nanoflakes. UV–vis diffuse reflectance spectra disclosed that the as-synthesized SnS2 nanoflakes had optical bandgaps in the range of about 2.21–2.25 eV. Besides, the photocatalytic performances of the as-synthesized SnS2 nanoflakes were evaluated by degrading methyl orange (MO) in deionized water under both the visible light (λ > 420 nm) and real sunlight irradiation. The results demonstrated that all the SnS2 products had high visible light photocatalytic activity, and the most efficient photocatalyst among them was the one synthesized at 200 °C for 0 h, which was able to achieve a MO degradation ratio of nearly 100% after 60 min illumination in the first cycle and 86% in the fifth cycle (each cycle lasted for 120 min). Moreover, the best sample also possessed much higher photocatalytic activity than the commercial Degussa P25 TiO2 photocatalyst under the real sunlight irradiation, and can be easily recovered from the suspension by filtration after the photocatalysis.

•A new visible-light-driven photocatalyst was synthesized using SnS2 and polyaniline.•The new catalyst can harvest more visible light.•The new catalyst showed enhanced separation and transfer of photogenerated charges.•The new catalyst can adsorb more Cr(VI).•The new catalyst had much higher activity than SnS2 in Cr(VI) reduction.Polyaniline (PANI) was adopted to modify SnS2 to develop a novel efficient visible-light-driven photocatalyst. SnS2/PANI composite was synthesized via first mixing of SnS2 and PANI in N,N-Dimethylformamide solution and subsequent evaporation of N,N-Dimethylformamide. The characterization by Raman and Fourier transform infrared spectroscopy demonstrated the production of SnS2/PANI composite. UV–vis diffuse reflectance absorbance spectra showed that the coupling with PANI enhanced the visible-light-absorbing capability of SnS2. The photoluminescence and electrochemical impedance spectra showed that SnS2/PANI composite was more efficient in the separation and transfer of photogenerated charges than SnS2. The photocatalytic tests showed that SnS2/PANI composite exhibited notably higher photocatalytic activity than SnS2 in reduction of aqueous Cr(VI) under visible-light (λ > 420 nm) irradiation (the rate of photocatalytic reduction of Cr(VI) by SnS2/PANI composite was nearly 4.2 times that by SnS2). The possible reasons underlying the enhanced photocatalytic activity of SnS2/PANI composite were also proposed.