TiO2 microspheres and TiO2/carbon quantum dots (CQDs) composites with different CQDs contents were successfully synthesized via solvothermal and in situ hydrothermal method. The structure and morphology of the prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscope (TEM). Results showed that carbon elements were successfully doped into the TiO2 lattice (C-TiO2) and CQDs were hybrid with C-TiO2 microspheres. The X-ray photoelectron spectroscope (XPS), valence band XPS (VB-XPS) and UV–vis diffuse reflectance spectra (DRS) analyses revealed that carbon doped into TiO2 microspheres could lead to local energy levels in the band structure and generate valence band tails to absorb visible light. The photocatalytic activities of these samples were evaluated by the photodegradation of Rhodamine B (RhB) under visible light irradiation. C-TiO2/CQDs samples presented an enhanced photocatalytic performance compared with pristine TiO2, which could be attributed to the present of CQDs, acting as adsorption sites for RhB molecules and charge separation centers to impede the recombination and prolong the life time of electron and hole pairs.

A series of Zn1−xMgxO nanoparticles with x=0 to 0.15 were prepared by auto combustion method using citric acid as the fuel and chelating agent. Structure, luminescence and photocatalytic properties were systematically investigated by means of X-ray diffraction, scanning electron microscopy, photoluminescence spectra, ultraviolet–visible absorbance measurement and photochemical reactions etc. The samples retained hexagonal wurtzite structure of ZnO and single phase below x=0.13, and the sizes of the nanoparticles were 60–70 nm. The photoluminescence spectroscopy demonstrated blue shift of ultraviolet emission with increasing Mg doping concentration. Both optical measurements of the as grown and Mg doped ZnO nanoparticles showed that the optical band gap could be modified from ~3.28 eV to 3.56 eV as the Mg content x increased from 0 to 0.13. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of methyl orange, and the results showed that the doping of Mg into ZnO nanoparticles could enhance photocatalytic activity compared to the undoped ZnO nanoparticles, which was attributed to increased band gap and superior textural properties. In addition, according to the PL and photocatalytic studies, the critical doping content of effective Mg in ZnO is up to 0.09.

•Ga dopant reduces the crystallite size of seed layer.•(0 0 2) is preferred direction of growth of nanorods.•Length and density of nanorods increases with increasing Ga dopant.•UV emission shows a blue shift of ∼7 nm.•Photocatalytic activity of nanorods is enhanced.ZnO nanorods have been successfully grown on Ga doped (0–5 wt%) ZnO seed layer by using simple hydrothermal method. Changing Ga content in the seed layers lead to formation of ZnO nanorods with high aspect ratio and increased density. The effects of Ga doped seed layer on optical and structural morphology of ZnO nanorods are investigated in detail by using Field-emission scanning electron microscope (FESEM), X-ray diffraction (XRD) and Photo luminescence spectroscopy (PL). It has been observed that the Ga doped seed layer strongly affected the structural morphology of ZnO nanorods. XRD results show that all the samples have hexagonal wurtzite shape and (0 0 2) is preferred direction of growth. The intensity of (0 0 2) peak increases with increasing Ga concentration in seed layer indicating that the Ga doped seed layer has promoted growth of nanorods along (0 0 2). SEM images show a decrease in diameter of ZnO nanorods with increasing Ga concentration in seed layer. The PL spectra of all the samples have two emission bands, UV and defect emission. UV emission shows a small blue shift with increasing Ga concentration in seed layer. The photocatalytic activity of as grown ZnO nanorods increases with aspect ratio (length) and density.

•ZnO nanowires are synthesized via a low-temperature (90 °C) hydrothermal route.•There exist graphitic carbons on the ZnO nanowires after vacuum annealing.•The PL intensity of ZnO nanowires with the graphitic carbons is significantly reduced.•The photocatalytic activity of ZnO nanowires with graphitic carbons is enhanced.ZnO nanowires were synthesized via a low-temperature (90 °C) hydrothermal route on glass substrates pre-deposited with a ZnO seed layer. The influence of different annealing ambient conditions (air or vacuum) on the structure, photoluminescence and photocatalytic activity of ZnO nanowires was investigated by Raman spectroscopy, X-ray diffraction, photoluminescence (PL) and photochemical reactions etc. It was found that there existed graphitic carbons on the surfaces of ZnO nanowires after vacuum annealing. The PL intensity of ZnO nanowires with the graphitic carbons was significantly reduced while the photocatalytic activity was enhanced, indicating that the graphitic carbons could decrease the recombination probability of photo-induced carriers.

ZnO co-doped with 2 at.% Sm and different Li concentration (0–7 at.%) powders were fabricated by the sol–gel method with 700 °C annealing. The effect of Li doping concentration on the structure and photoluminescence (PL) of ZnO powders doped with 2 at.% Sm was investigated. Based on the balance of structure and valence, with the help of Li doping (1, 2 at.%) into ZnO powders doped with 2 at.% Sm, Sm3+ ions enter ZnO crystal lattice and induce the characteristic Sm3+ emission peaks by the ultra-violet (UV) excitation (278 nm). Especially, when the Li doping concentration is 2 at.%, the sample has the most efficient Sm characteristic emission line. However, Li will hinder the substitution of zinc location by Sm3+ when the Li doping concentration is above 3 at.%, which results in the disappearance of the characteristic samarium emission lines.

Sn-doped ZnO (SZO) thin films are deposited by sol–gel dip-coating method with Sn content at 0 at.% and 1–15 at.% with an increment of 2 at.%. The structure and luminescence of the films are investigated. X-ray diffraction results indicate that all the SZO samples show preferential orientation along the (002) direction, and the scanning electron microscope exhibits that the surface morphology of the films change from nanoparticles to nanorods with increasing Sn concentration. X-ray photoelectron spectroscopy reveals that Sn exists as valence of +4 in the matrix. The photoluminescence peaks at 381 and 398 nm are observed in all the samples. The ratio of intensity of peak at 381 nm to that of peak at 398 nm differed markedly. The intensity of peak at 398 nm might be due to the response for the Sn atoms, while the intensity of peak at 381 nm is probably related to the quantum size effect.

•Novel SnO2@g-C3N4 core-shell structures were successfully synthesized.•The core-shell structures exhibited enhanced visible light photocatalytic activity.•The enhanced photocatalytic activity was due to synergic action of SnO2 and g-C3N4.SnO2@g-C3N4 core-shell structures were successfully synthesized by simple calcination of SnO2 microspheres and urea in a muffle furnace. The investigation of morphologies and microstructures showed that g-C3N4 was wrapped tightly on the surface of SnO2 microspheres with large intimate interface contact areas between the g-C3N4 shells and SnO2 cores. The X-ray photoelectron spectroscopy results and photoluminescence spectra demonstrated that the intimate interface contacts could facilitate the transfer and separation of the photogenerated charge carriers at their interface, thus the recombination of the photogenerated electron-hole pairs was impeded. The photocatalytic activity of the synthesized composites was evaluated by the photodegradation of methyl orange under visible light irradiation. It was found that SnO2@g-C3N4 exhibited higher photodegradation rate (k = 0.013 min−1) than that of g-C3N4 (k = 0.008 min−1) and pure SnO2. The enhanced photocatalytic activity could be attributed to the synergic action of SnO2 and g-C3N4.