Junli Chen

Homogeneous Pd nanoparticles produced in direct reactions: green synthesis, formation mechanism and catalysis properties

The direct reactions between ascorbic acid (AA) and palladium salts can produce homogeneous Pd nanoparticles on a large scale by grinding or shaking the two reactants together for ca. 2 minutes at room temperature. The size of homogeneous Pd nanoparticles can be tuned conveniently by using different palladium salts as precursors in the reactions without adding any solvent and organic protectors. Compared to Pd nanoparticles with much smaller sizes of ca. 2.7 nm produced by grinding a solid mixture of AA and Pd(CH3COO)2, homogeneous Pd nanoparticles of 35.6 ± 5 nm can be generated in the direct reaction between AA and Pd(NO3)2·2H2O. It was found that AA can reduce Pd2+ to Pd0 to form Pd nanoparticles directly, accompanied by its oxidation to 2,3-diketogulonic acid (2,3-DKG) and a series of fragment species of 2,3-DKG simultaneously. The small amount of crystalline water in Pd(NO3)2·2H2O can promote the formation of Pd nanoparticles dramatically, compared to the reactions conducted with Pd(CH3COO)2, Pd(NO3)2 and PdCl2 without crystalline water. Based on the experimental results, a two-step reaction mechanism is proposed to understand the formation of Pd nanoparticles. The quasi solid-state features of the direct reactions could lead to defects of high concentration on the surface of the as-prepared Pd nanoparticles, which can be applied to the catalysis of the Suzuki reaction immediately after their formation in the reactions.

Asymmetric supercapacitors based on a NiCo2O4/three dimensional graphene composite and three dimensional graphene with high energy density

A NiCo2O4 nanoparticle/three dimensional porous graphene (NiCo2O4/3D-G) composite was synthesized through a facile hydrothermal method combined with subsequent annealing treatment. X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy analyses indicate that the NiCo2O4 nanoparticles were tightly anchored on the graphene sheets in the NiCo2O4/3D-G composite. When used as a supercapacitor electrode material, the obtained NiCo2O4/3D-G displayed a high specific capacitance of 2300 F g−1 at 1.0 A g−1 in 2.0 M KOH electrolyte. The asymmetric supercapacitor utilizing NiCo2O4/3D-G and 3D-G as positive and negative electrodes, respectively, delivered a high energy density of 73.8 W h kg−1 with a power density of 800 W kg−1 and long cycle stability (94.3% capacitance retention after 5000 cycles). The excellent supercapacitive performance of the NiCo2O4/3D-G can be ascribed to the synergistic effect of the porous and conductive three-dimensional cross-linking 3D-G and the high pseudocapacitive performance of the NiCo2O4 nanoparticles.

A PPy/Cu2O molecularly imprinted composite film-based visible light-responsive photoelectrochemical sensor for microcystin-LR

In this study, a visible light-responsive photoelectrochemical (PEC) sensor based on a PPy/Cu2O molecularly imprinted composite film for microcystin-LR (MC-LR) has been fabricated. Uniform Cu2O nanoparticles were electrodeposited on a pretreated indium-doped tin oxide-coated glass (ITO) by carefully controlling the deposition process and used as a photocatalyst to produce photocurrent under visible light. Subsequently, molecularly imprinted polypyrrole (PPy) was modified on the surface of the Cu2O/ITO electrode by an electropolymerization process, which created a certain amount of special recognition sites to enhance the selectivity of the electrode to MC-LR. PEC molecular imprinting sensors were used to rapidly analyze MC-LR concentration by determining changes in photocurrent density. The results showed that the change of photocurrent density was linearly proportional to the logarithm of the MC-LR concentration over the ranges from 1.0 ng L−1 to 100 ng L−1 and from 100 ng L−1 to 10.0 μg L−1 with a low detection limit of 0.23 ng L−1 (S/N = 3). Moreover, the PEC sensors exhibited specific selectivity to MC-LR when exposed to certain concentrations of interfering solutions. The constructed PEC sensors demonstrated good applicability in local water systems; this suggested that this promising application of integrating PEC and molecular imprinting technology could be applied to detect other contaminants of emerging concern.