Photocatalytic degradation of bisphenol A by temperature-sensitive magnetic hydrogel with enhanced service life.

Easy diffusion and low reusability limit the practicality of photocatalysts. In this study, a hollow sphere (HS) heterojunction was synthesized based on oxygen-doped carbon nitride (OCN) and layered double hydroxides (LDHs). A thermosensitive HS hydrogel (HS Gel) was prepared by mixing HS with N-isopropylacrylamide. Bisphenol A (BPA), being widely manufactured and used in commercial and domestical products and its high toxicity, was chosen as the target pollutant to demonstrate the photocatalytic ability and practicality of the HS Gel. HS Gel presented effective BPA degradation (95% degradation in 70 mins, 4.2 × 10-2 min-1 of kobs) at ambient temperature which is much better than kobs = 1.8 × 10-2 min-1 of OCN and kobs = 0.08 × 10-2 min-1 of LDH), and increased by two-fold the recycling service life (retention of >80% degradation efficiency after 13 usage cycles) compared to other carbon-based photocatalysts (retention of >80% degradation efficiency after 5-6 usage cycles). This is due to its multifunctional characteristics (magnetic property and thermal sensitivity). Under ambient temperature, the hydrophilic HS Gel swelled in the aqueous solution, which promoted the photocatalytic reaction between HS and BPA in the gel state. After the reaction, the HS Gel was subjected to shrinkage by high temperature heating to enhance the mechanical strength for recovery. The magnetic recovery was realized by the paramagnetic properties of layered double oxide to reduce environmental interference. Detailed studies of HS gel related to enhanced service life were conducted including structural changes, catalyst leaking and magnetic changing. A new kind of type Ӏ plus Z-scheme mechanism was also proposed based on the Kubelka-Munk equation, UV diffuse reflectance spectroscopy and Mott-Schotty technique.

Light-enhanced transparent hydrogel for uric acid and glucose detection by four different analytical platforms.

The lack of solid-phase media limits the portability of colorimetric sensing platforms. In this study, a series of transparent polyvinyl alcohol (PVA) hydrogels encapsulated antimony tin oxide nanoparticles (ATO NPs) and 3,3',5,5'-tetramethylbenzidine (TMB) were developed as the solid-phase sensing media for glucose and uric acid. Under the conditions of H2O2 and UV light, the hydrogel presented a multicatalytic ability (photo Fenton-like and peroxidase-like activities), which accelerated the oxidation of TMB, turning the hydrogel from colorless to blue and finally enhancing the detection signal. The plasticity of the hydrogel allowed it to be designed into various shapes (membrane, microsphere etc.) to adapt multiple detection platforms (a liquid/solid-phase UV spectrophotometer, a NanoPhotometer, and smartphone spectroscopy). The hydrogel sensing media exhibited excellent tunability and enhanced the photocatalytic ability. The proposed material was successfully applied to detect glucose and uric acids in real samples by four detection platforms to evaluate its practicability.

Noble metal-free 0D-1D NiSx/CdS nanocomposites toward highly efficient photocatalytic contamination removal and hydrogen evolution under visible light.

The development of stable noble metal-free photocatalysts with efficient separation and transportation of the photogenerated electrons-holes is of crucial importance for promoting the application of photocatalysis technology. Herein, we propose an electron transfer strategy by reasonable design and fabrication of novel 0D NiSx nanosheets as a co-catalyst on the surface of 1D CdS nanorods (CdS-NRs) to enhance photocatalytic hydrogen evaluation and contamination (Cr(vi), rhodamine B and bisphenol A) removal in water. Under visible light irradiation, the 0D-1D NiSx/CdS-NR nanocomposite with 1.5% NiSx loading gave a hydrogen evolution rate of 5.98 mmol h-1 g-1, which is about 5.3 times and 1.9 times higher than that of the native CdS-NRs and the optimal 1% Pt/CdS-NRs, respectively. Notably, good stability in the recycling test and a high apparent quantum efficiency of about 69.9% at 420 nm were also obtained. The 1.5% NiSx/CdS-NRs exhibited enhanced photocatalytic contamination degradation efficiency of about 2 times higher than pure CdS-NRs. In this hybrid photocatalyst, 0D NiSx nanosheets came into intimate interfacial contact with the surface of 1D CdS-NRs and played a similar role as noble metals, which could effectively improve the separation, transportation efficiencies and lifetime of photogenerated charge, and thus enhance the photocatalytic performance of CdS-NRs with more efficient conversion of solar energy. This work shows not only a possibility for the utilization of noble metal-free NiSx as a co-catalyst in the photocatalysis, but also provides new insight into the design and fabrication of high-performance composite photocatalysts (such as NiSx/g-C3N4 and NiSx/Zn3In2S6).

Ferrocene-modified carbon nitride for direct oxidation of benzene to phenol with visible light.

Ferrocene moieties were heterogenized onto carbon nitride polymers by a covalent -C=N- linkage bridging the two conjugation systems, enabling the merging of the redox function of ferrocene with carbon nitride photocatalysis to construct a heterogeneous Photo-Fenton system for green organocatalysis at neutral conditions. The synergistic donor-acceptor interaction between the carbon nitride matrix and ferrocene group, improved exciton splitting, and coupled photocatalytic performance allowed the direct synthesis of phenol from benzene in the presence of H2 O2 under visible light irradiation. This innovative modification method will offer an avenue to construct functionalized two-dimensional polymers useful also for other green synthesis processes using solar irradiation.

Metal-free activation of H2O2 by g-C3N4 under visible light irradiation for the degradation of organic pollutants.

Semiconducting carbon nitride materials were successfully prepared via a thermal poly-condensation of dicyandiamide as a precursor at >500 °C. The resulting materials were investigated as metal-free catalysts for the activation of H(2)O(2) with visible light under mild conditions, using the decomposition of Rhodamine B (RhB) in aqueous solution as a model reaction. Results revealed that carbon nitride catalysts can activate H(2)O(2) to generate reactive oxy-radicals under visible light irradiation without employment of any metal additives, leading to the mineralization of the dye. Factors affecting the degradation of organic compounds are pH values and the concentration of H(2)O(2). Recycling of the catalyst indicated no obvious deactivation during the entire catalytic reaction, indicating good (photo)chemical stability of metal-free polymeric carbon nitride photocatalysts for environmental purification. This study demonstrated a promising approach for the activation of green oxidant, hydrogen peroxide, by the newly-developed polymer photocatalysts for environmental remediation and oxidation catalysis.

Visible light-sensitive ZnGe oxynitride catalysts for the decomposition of organic pollutants in water.

A ZnGe oxynitride semiconductor was prepared by a solid-state reaction using GeO(2) and ZnO under NH(3) flow. The catalyst was used as a visible-light photocatalyst for the decomposition of organic compounds in polluted water. The physicochemical properties of the synthesized ZnGe oxynitride photocatalysts were characterized by several techniques, and aqueous photocatalytic activity was evaluated via the decomposition of model organic compounds including Rhodamine B, Methyl orange, Methylene blue, 4-chlorophenol, and salicylic acid. The results demonstrate that ZnGe oxynitride can photocatalytically oxidize organic pollutants in aqueous solution under visible light irradiation, suffering no obvious catalyst deactivation during reaction testing. The possible active species in the photocatalytic process are also discussed.