Yuanzhi Hong

Synthesis of a novel ionic liquid modified copolymer hydrogel and its rapid removal of Cr (VI) from aqueous solution

A novel ionic liquid modified copolymer hydrogel (PAMDA) was successfully synthesized by a simple water solution copolymerization using acrylamide (AM), dimethyldiallylammonium chloride (DADMAC) and ionic liquid (1-allyl-3-methylimidazolium chloride; [Amim]Cl) as copolymerization monomers. The structure and morphology of as-prepared copolymer hydrogel PAMDA were confirmed by Fourier transform infrared (FT-IR), field-emission scanning electron microscope (FE-SEM) and thermogravimetric analysis (TG). The copolymer hydrogel was applied as a novel adsorbent for the rapid removal of Cr (VI) from aqueous solution. The effects of several parameters such as the content of ionic liquid [Amim]Cl, solution pH, contact time, adsorbent dosage and initial Cr (VI) concentration on the adsorption were also investigated. The modification of [Amim]Cl significantly enhanced Cr (VI) adsorption. The adsorption equilibrium data fitted with Langmuir isotherm model better than Freundlich isotherm model. The maximum adsorption capacity for Cr (VI) ions was 74.5 mg L(-1) at 323 K based on Langmuir isotherm model. The removal rate could reach 95.9% within 10 min at 323 K and the adsorption process of Cr (VI) on PAMDA was well described by the pseudo-second-order kinetic model. The activation energy of adsorption was further investigated and found to be 1.094 kJ mol(-1), indicating the adsorption of Cr (VI) onto PAMDA was physisorption.

Fabrication of novel Z-scheme InVO4/CdS heterojunctions with efficiently enhanced visible light photocatalytic activity

Novel Z-scheme InVO4/CdS heterojunction photocatalysts have been successfully synthesized for the first time via a microwave-assisted process, followed by a mild hydrothermal method. The crystal structures, morphologies and sizes, chemical compositions and optical properties of the prepared photocatalysts were characterized via X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), UV-vis diffuse reflectance spectroscopy (DRS), and photocurrent measurements. Results showed that the prepared InVO4/CdS heterojunctions were composed of about 15 nm InVO4 nanoparticles and 1.5 μm CdS microspheres, and all heterojunctions exhibited good photoabsorption in the visible light region. The photocatalytic activity of the obtained samples was carefully evaluated via the degradation of rhodamine B (RhB) and ciprofloxacin (CIP) under visible light irradiation (λ > 420 nm). Compared to that of bare InVO4 and CdS, the InVO4/CdS heterojunctions exhibited significantly enhanced photocatalytic activity for RhB and CIP degradation. Moreover, the 40 wt% InVO4-coupled CdS composite displayed the highest catalytic efficiency for RhB photodegradation, which is about 59.4 and 4.8 times higher than that of pure InVO4 and CdS, respectively. In addition, the active species trapping experiment and electron spin resonance (ESR) measurement demonstrated that h+ and ˙O2− radicals were the predominant active species in the photocatalytic reaction process. Furthermore, the possible enhanced photocatalytic mechanism of InVO4/CdS heterojunctions was also proposed based on the band position measurements and ESR analysis.

Hydrothermal synthesis of g-C3N4/CdWO4 nanocomposite and enhanced photocatalytic activity for tetracycline degradation under visible light

Novel visible light responsive g-C3N4/CdWO4 photocatalysts were formed by an in situ growth mechanism and employed in the degradation of a tetracycline (TC) antibiotic. The as-prepared composites were studied by several characterization techniques. Results revealed that the interface interaction between CdWO4 and g-C3N4 was recognized via CdWO4 nanorod loading on the surface of the layered g-C3N4, improving the separation and transfer of the photoexcited hole and electron pairs and restraining the recombination rate of photoinduced charge carriers. As a result, the photocatalytic activity of the g-C3N4/CdWO4 was enhanced in comparison with pure g-C3N4 and CdWO4 for TC degradation under visible light irradiation. Among the as-synthesized samples, the 80 wt% g-C3N4/CdWO4 photocatalyst showed optimal photocatalytic efficiency, which was about 4.0 and 20.0 times higher than that of bare g-C3N4 and CdWO4 under visible light irradiation, respectively. Significantly, the g-C3N4/CdWO4 composites exhibited better stability even after four successive cycles for TC degradation under visible light irradiation. Based on the active radical trapping and electron spin resonance (ESR) experiments, the possible mechanism of enhancing photocatalytic activity under visible light irradiation (λ > 420 nm) was proposed, to lead to further improvement in environmental remediation.

Carbon quantum dot decorated hollow In2S3 microspheres with efficient visible-light-driven photocatalytic activities

Carbon quantum dot (CQDs) decorated hollow In2S3 microspheres were firstly synthesized by a facile hydrothermal method. CQDs with an average size of 5 nm were attached on the surfaces of hollow In2S3 microspheres. The photocatalytic activities of the as-prepared samples were investigated by the photocatalytic degradation of methyl orange under visible light, and the 3 wt% CQDs/In2S3 sample presented the most efficient photocatalytic activity which was almost 3 times the pure In2S3 sample. On the basis of the active species trapping experiment and ESR analysis, holes and superoxide radicals were proved to be the main active species in the photocatalytic degradation process, and a possible reaction mechanism was proposed.

Controllable TiO2 heterostructure with carbon hybrid materials for enhanced photoelectrochemical performance

In TiO2 both advantages (stability and low cost) and disadvantages (large bandgap) coexist, so how to optimize a bare TiO2 electrode is a continuous hot topic for the construction of suitable photoelectrochemical (PEC) devices based on TiO2 for water splitting. This paper reports a facile and simple fabrication of a TiO2/RGO/C3N4 photoelectrode for PEC splitting of water. Its heterostructure configuration has been characterized and confirmed by XRD, Raman spectroscopy, XPS, TEM and STEM. The introduction of both RGO and C3N4 film onto the surface of TiO2 is mainly due to the fact that C3N4 has a strong photoelectric ability to respond to visible light and RGO plays an important role in the fast transfer of photogenerated charges across interfaces. Photocurrent and monochromatic incident photon-to-photocurrent efficiency (IPCE) of the titled heterostructure have been obviously improved, and the IPCE value (0.5 V vs. AgCl/Ag) of TiO2/RGO/C3N4 was estimated to be up to 28% at a wavelength of 400 nm.

Effective bandgap narrowing of Cu–In–Zn–S quantum dots for photocatalytic H2 production via cocatalyst-alleviated charge recombination

The development of single-component photocatalysts with narrow bandgaps (2.0–3.0 eV) has been one of the most important goals for photocatalytic H2 production, for which I–III–VI multinary sulfides play an important role due to their widely tunable composition-dependent bandgap. However, simultaneous bandgap narrowing and photocatalytic activity enhancement in the I–III–VI sulfides are often difficult to achieve due to increased defect states. Here, a series of Cu–In–Zn–S quantum dots (QDs) were synthesized by a facile hydrothermal method focusing on a more profound understanding of bandgap tuning and the subsequent effect on the photocatalytic process by controlling the Cu content. The bandgap of the QDs can be effectively tuned from 2.90 eV to 1.98 eV with an increasing Cu : In ratio from 0.05 : 10 to 2.5 : 10 and a color change from light yellow to dark red. The QDs show photocatalytic H2 production activity even without any cocatalyst, but it quickly starts to decrease with the Cu/In ratio over 0.1 : 10 (bandgap of 2.59 eV), which highly limits the potential for visible light photocatalysis. Interestingly, Pt-loading effectively enhanced not only the tolerance of Cu incorporation, but also enabled a high H2 production activity even with further bandgap narrowing down to ∼2 eV. The best photocatalytic performance of 456.4 μmol h−1 g−1 was achieved for the Cu : In : Zn ratio of 1 : 10 : 5 with a bandgap of 2.27 eV. This increased tolerance of Cu content may result from a combined effect of charge separation by Pt as the cocatalyst that alleviated the Cu-induced charge recombination. The enhanced charge separation was proved by the photoluminescence quenching of the QDs with the cocatalyst. Electrochemical impedance spectroscopy was further used to study the charge separation properties of this photocatalytic system. This is the first observation of the cocatalyst-enhanced tolerance of Cu resulting from the competition of cocatalyst-induced charge separation and defect-induced charge recombination in multinary sulfides, which provides an interesting view and design guideline for the development of narrow bandgap photocatalysts.

One-Step Nickel Foam Assisted Synthesis of Holey G-Carbon Nitride Nanosheets for Efficient Visible-Light Photocatalytic H2 Evolution

Graphitic carbon nitride (g-C3N4) with layered structure represents one of the most promising metal-free photocatalysts. As yet, the direct one-step synthesis of ultrathin g-C3N4 nanosheets remains a challenge. Here, few-layered holey g-C3N4 nanosheets (CNS) were fabricated by simply introducing a piece of nickel foam over the precursors during the heating process. The as-prepared CNS with unique structural advantages exhibited superior photocatalytic water splitting activity (1871.09 μmol h-1 g-1) than bulk g-C3N4 (BCN) under visible light (λ > 420 nm) (≈31 fold). Its outstanding photocatalytic performance originated from the high specific surface area (240.34 m2 g-1) and mesoporous structure, which endows CNS with more active sites, efficient exciton dissociation, and prolonged charge carrier lifetime. Moreover, the obvious upshift of the conduction band leads to a larger thermodynamic driving force for photocatalytic proton reduction. This methodology not only had the advantages for the direct and green synthesis of g-C3N4 nanosheets but also paved a new avenue to modify molecular structure and textural of g-C3N4 for advanced applications.