Ke Dai

Fullerene C70–TiO2 hybrids with enhanced photocatalytic activity under visible light irradiation

Fullerene C70 modified TiO2 (C70–TiO2) hybrids were fabricated through a hydrothermal method from titanium sulfate and functionalized C70. The structures of the synthesized hybrids were characterized by X-ray diffraction, UV-vis diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller surface area measurements, matrix-assisted laser desorption/ionization-time of flight-mass spectrometry and photoluminescence spectroscopy. The experimental results indicated that the introduction of C70 slightly reduces the crystallite size of TiO2 while extending its adsorption edge to the visible light region. C70 dispersed on the surface of TiO2 nanoparticles with covalent bonding, which generated strong interactions between the functionalized C70 and TiO2. The O2˙−, ˙OH and h+ are active species which were proved by the trapping experiment. The photocatalytic degradation efficiency of sulfathiazole over C70–TiO2 hybrids is higher than that over pure TiO2, C60–TiO2, and a mechanical mixture of C70 and TiO2 under visible light irradiation. The excellent visible light-induced activity is rationalized by the results of photoluminescence spectroscopy; i.e., the intensities of emissions from C70–TiO2 hybrids were found to be weaker than those from pure TiO2 and C60–TiO2 hybrid.

Enhanced visible-light-driven photoactivities of single-walled carbon nanotubes coated with N doped TiO2 nanoparticles

A two-step hydrothermal method is used to prepare N doped single-walled carbon nanotube–TiO2 (SWCNT–N/TiO2) hybrids with different contents of SWCNTs from 1.25 wt% to 10 wt%. The photocatalysts were characterized by X-ray diffraction analysis, UV-vis diffuse reflectance spectroscopy, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The UV-vis diffuse reflectance spectra show an apparent enhancement of absorption throughout the visible light region. Raman spectroscopy further confirms the chemical interaction between N/TiO2 and SWCNTs in the hybrid. SWCNT–N/TiO2 hybrid presents a superior photocatalytic activity to DWCNT–N/TiO2 (N doped double-walled carbon nanotube–TiO2) and MWCNT–N/TiO2 (N doped multi-walled carbon nanotube–TiO2) based on the results of the photocatalytic degradation of sulfathiazole under visible light irradiation, which is attributed to the synergetic effects of SWCNT modification and N doping. N doping induces visible light absorption by either introducing localized electronic states within the band gap or contributing electrons to the valence band and metal-like SWCNT can act as an electron conductor to facilitate the fast injection of the photogenerated electrons into the conduction band of N/TiO2, leading to significantly enhanced visible-light-driven photocatalytic activity.

Metal-free inactivation of E. coli O157:H7 by fullerene/C3N4 hybrid under visible light irradiation

Interest has grown in developing safe and high-performance photocatalysts based on metal-free materials for disinfection of bacterial pathogens under visible light irradiation. In this paper, the C60/C3N4 and C70/C3N4 hybrids were synthesized by a hydrothermal method, and characterized by X-ray diffraction (XRD), UV-vis diffuse reflection spectroscopy (UV-vis DRS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and high revolution transmission electron microscope (HRTEM). The performance of photocatalytic disinfection was investigated by the inactivation of Escherichia coli O157:H7. Both C60/C3N4 and C70/C3N4 hybrids showed similar crystalline structure and morphology with C3N4; however, the two composites exhibited stronger bacterial inactivation than C3N4. In particular, C70/C3N4 showed the highest bactericidal efficiency and was detrimental to all E. coli O157:H7 in 4h irradiation. Compared to C3N4, the enhancement of photocatalytic activity of composites could be attributed to the effective transfer of the photoinduced electrons under visible light irradiation. Owing to the excellent performance of fullerenes (C60, C70)/C3N4 composites, a visible light response and environmental friendly photocatalysts for disinfection were achieved.

Enhanced visible light photocatalytic activity of TiO2 assisted by organic semiconductors: a structure optimization strategy of conjugated polymers

The search for high-efficient TiO2-based heterojunction photocatalyst for photocatalytic H2 evolution and pollutant removal remains a great challenge. In this study, linear conjugated polymer B-BT-1,4-E consisting of alternating electron donor and electron acceptor was incorporated on the surface of TiO2 to form a binary composite in the facile in situ strategy. B-BT-1,4-E/TiO2 exhibited superior photocatalytic activity under visible light irradiation (λ ≥ 420 nm). The hydrogen evolution rate (HER) of 16.7% B-BT-1,4-E/TiO2 reached 220.4 μmol h−1 without additional noble metal (Pt), and the optimized 13.3% B-BT-1,4-E/TiO2 also displayed outstanding CIP degradation efficiency with a kinetic constant of 0.232. Based on extensive characterization results from UV-Vis diffused reflectance spectra (DRS), electron spin resonance (ESR), photocurrent, electrochemical impedance spectroscopy (EIS) and photoluminescence (PL), the enhanced photocatalytic activity of B-BT-1,4-E/TiO2 heterojunction can be attributed to broader visible light absorption range, faster charge separation and transfer. Moreover, a reasonable photocatalytic mechanism is also proposed. In comparison to reported CMP(BBT)/TiO2, HER and kinetic constants of CIP degradation with B-BT-1,4-E/TiO2 as the photocatalyst were increased by 7.3 times and 3.1 times, respectively. This study demonstrated that intrinsic merits of conjugated polymers made them promising candidates for exploring more efficient organic semiconductor–inorganic semiconductor heterojunction photocatalysts.

Simple fabrication of Fe3O4/C/g-C3N4 two-dimensional composite by hydrothermal carbonization approach with enhanced photocatalytic performance under visible light

The construction of a multifunctional two-dimensional (2D) composite photocatalyst is of great significance because such a composite can exhibit enhanced catalytic performance and improved practical usability in contrast to a single component catalyst. Herein, a ternary photocatalyst composed of g-C3N4, a carbon layer (C), and Fe3O4 nanoparticles was successfully synthesized by a facile one-pot hydrothermal carbonization (HTC) method from g-C3N4, glucose, and FeCl3. The resultant composite, Fe3O4/C/g-C3N4, had an ordered 2D heterostructure and exhibited enhanced visible-light-driven photocatalytic performances and good magnetic recyclability. The kobs for Cr(VI) photoreduction (or dimethoate photodegradation) over Fe3O4/C/g-C3N4 was 20.9-fold (or 2.1-fold) of that over g-C3N4. Comparative study of Fe3O4/C/g-C3N4, C/g-C3N4, and g-C3N4 on their optoelectronic properties revealed that this enhanced photocatalytic activity was mainly due to rapid photogenerated electron transport from the g-C3N4 component to carbon and/or Fe3O4, which effectively suppressed the recombination of photogenerated electrons and holes. In addition, the good surface adsorption capacity of the carbon component towards Cr(VI) also contributed to Cr(VI) photoreduction over Fe3O4/C/g-C3N4. Finally, a reasonable photocatalytic reaction mechanism of Fe3O4/C/g-C3N4 was proposed based on the results of trapping experiments. This study is not only limited to developing a high-performance g-C3N4 based photocatalyst, but also expected to provide a green, facile, and cost-efficient strategy to combine 2D materials with a carbonaceous layer and other functional components for a multifunctional system.

Photocatalytic Degradation of Sulfonamides over the Short Multi-Walled Carbon Nanotube-TiO2 Hybrid

The short multi-walled carbon nanotube-TiO2 (SMWNT-TiO2) hybrid was synthesized via direct growth of TiO2 nanoparticles on the surface of the functionalized SMWNTs by the hydrothermal treatment and utilized as the photocatalyst in the sulfonamides degradation under UV light irradiation. The photodegradation efficiency of sulfonamides was examined by HPLC technique, which demonstrates that sulfonamides can be readily degraded under UV light irradiation. However, the four sulfonamides have different degradation rates, which is in the order of sulfadimidine > sulfanilamide > sulfamethoxazole > sulfathiazole. These experimental results can be attributed to the point charge of the atoms in the sulfonamide molecule and its adsorption on the surface of the SMWNT-TiO2 hybrid.

Photocatalytic Degradation of Carbaryl over Novel MWNT-TiO2 Nanocomposite under Visible Light Irradiation

The MWNT-TiO2 nanocomposite was synthesized via direct growth of TiO2 nanoparticles on the surface of the functionalized MWNTs by the hydrothermal treatment and utilized as the photocatalyst in the carbaryl degradation under both visible light and UV light irradiation. Visible-light-driven activity and enhanced UV-light-driven activity are both achieved as the composite MWNTs with TiO2 can efficiently enhance the light absorption and charge separation and then photocatalytic activity. The photodegradation efficiency of carbaryl was examined by HPLC and IC techniques, which demonstrates that carbaryl can be readily degraded under visible light irradiation. Based on the obtained experimental results, assisted with the computer simulation of carbaryl molecule on PM3 level, it is presumed that the degradation of carbaryl starts with the break of N21-C23 and C19-N21 bonds and ends in the generation of naphthalen-1-ol before the ring-opening reaction.