Self-assembled three-dimensional Pd/MoS2/reduced graphene oxide nanocatalyst: A case for homogeneous leaching mechanism

Recent advances in biological molecule detection based on a three-dimensional graphene structure

Graphene has become an attractive material in the field of electrochemical detection owing to its unique electrical properties. Although the simple stacking structures of two-dimensional (2D) graphene sheets can provide excellent detection properties, a macroscopic three-dimensional (3D) structure needs to be constructed to enhance its functional properties. Graphene with a 3D structure has elegant functions, unlike graphene with a 2D structure. These properties include a large specific surface area, easy loading of nanomaterials with electrocatalytic and redox functions, and so on. Herein, we outline the preparation methods (self-assembly, chemical vapor deposition, templates, and 3D printing) for 3D graphene structures for obtaining excellent detection performance and applications in detecting biological molecules, bacteria, and cells. Furthermore, this review focuses on the improvement of the detection performance and enhancement of the applicability of graphene-based electrochemical sensors. We hope that this article will provide a reference for the future development of electrochemical sensors based on 3D graphene composites.

Green synthesis of reduced graphene oxide/chitosan/gold nanoparticles composites and their catalytic activity for reduction of 4-nitrophenol

Gold nanoparticles (AuNPs) have attracted extensive attention in the past few years due to their unique properties and great potential application in catalysis. However, the application of AuNPs remains a significant challenge due to the lack of high efficiency and stability caused by aggregation. Immobilization of AuNPs on appropriate support shows promising results in avoiding aggregation and improving catalytic activity. In this work, reduced graphene oxide/chitosan/gold nanoparticles (rGO/CHS/AuNPs) composites were prepared using chitosan with different molecular weights (MW) as a reducing agent and stabilizer, and characterized by FT-IR, XRD, XPS, SEM, FESEM, EDS, TEM, HRTEM, and TGA. The preparation conditions of rGO/CHS/AuNPs composites, including chitosan MW, CHS/GO mass ratio, reaction temperature and time, and HAuCl₄ concentration were investigated in detail. The results indicated that reduction activity of chitosan for GO increased with the decrease of chitosan MW. The C/O ratio of rGO reduced by low molecular weight chitosan (LMWC) with viscosity-average molecular weight (Mv) of 21 kDa was 6.34. Small spherical AuNPs were uniformly immobilized on the rGO surface. The particle size of AuNPs increased from 9.29 to 13.03 nm as chitosan MW decreased from 465 to 21 kDa. The rGO/CHS/AuNPs showed good catalytic activity for the reduction of 4-NP in the presence of NaBH₄. The catalytic activity of rGO/CHS/AuNPs was closely related to chitosan MW. rGO/CHS/AuNPs synthesized by LMWC with Mv of 21 kDa showed the highest kinetic rate constant of 0.2067 min^-1. The results of this experimental study could be useful in the development of effective catalysts for the reduction of aromatic nitro compounds.

Recent developments in hydrogels containing copper and palladium for the catalytic reduction/degradation of organic pollutants

The elimination of toxic and hazardous contaminants from different environmental media has become a global challenge, causing researchers to focus on the treatment of pollutants. Accordingly, the elimination of inorganic and organic pollutants using sustainable, effective, and low-cost heterogeneous catalysts is considered as one of the most essential routes for this aim. Thus, many efforts have been devoted to the synthesis of novel compounds and improving their catalytic performance. Recently, palladium- and copper-based hydrogels have been used as catalysts for reduction, degradation, and decomposition reactions because they have significant features such as high mechanical strength, thermal stability, and high surface area. Herein, we summarize the progress achieved in this field, including the various methods for the synthesis of copper- and palladium-based hydrogel catalysts and their applications for environmental remediation. Moreover, palladium- and copper-based hydrogel catalysts, which have certain advantages, including high catalytic ability, reusability, easy work-up, and simple synthesis, are proposed as a new group of effective catalysts.

The elimination of toxic and hazardous contaminants from different environmental media has become a global challenge, causing researchers to focus on the treatment of pollutants.

Cobalt Nanoparticles Supported on Reduced Amine-Functionalized Graphene Oxide for Catalytic Reduction of Nitroanilines and Organic Dyes

In our study, a simple strategy to fabricate an efficient cobalt-based nanocatalyst is reported. The as-fabricated cobalt nanoparticles (Co NPs) that supported on reduced amine-functionalized graphene oxide (Co@RGO-NH[Formula: see text] have been fabricated through reduction of Co[Formula: see text] and GO-NH2 by sodium borohydride under mild conditions. The morphology, elemental analysis, chemical composition, surface area and magnetic property of the as-fabricated Co@RGO-NH2 nanocatalyst have been investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) and vibrating sample magnetometer (VSM), respectively. Characterization showed that Co@RGO-NH2 nanocatalyst possesses a high surface area (232.05 m2/g) and good magnetic property. Obviously, the as-fabricated Co@RGO-NH2 nanocatalyst exhibited a fascinating catalytic activity towards the catalytic reduction of different substituted nitro anilines pollutants ([Formula: see text]-nitroaniline, [Formula: see text]-nitroaniline and [Formula: see text]-nitroaniline), as well as, the degradation of cationic methylene blue and anionic Congo red dyes. Furthermore, the reused Co@RGO-NH2 nanocatalyst has shown high catalytic activity for all the catalytic reactions even after the fifth cycle, asserting the high stability of the as-fabricated heterogeneous catalyst.

Polyvinylpyridine-Supported Palladium Nanoparticles: An Efficient Catalyst for Suzuki–Miyaura Coupling Reactions

Palladium nanoparticles (Pd NPs) synthesized by the metal vapor synthesis technique were supported on poly(4-vinylpyridine) 2% cross-linked with divinylbenzene (Pd/PVPy). Transmission electron microscopy revealed the presence of small metal nanoparticles (dm = 2.9 nm) highly dispersed on the PVPy. The Pd/PVPy system showed high catalytic efficiency in Suzuki-Miyaura carbon–carbon coupling reactions of both non-activated and deactivated aromatic iodides and bromides with aryl boronic acids, carried out under an air atmosphere. The high turnover of the catalyst and the ability of the PVPy resin to retain active Pd species are highlighted. By comparing the catalytic performances of Pd/PVPy with those observed by using commercially available Pd-based supported catalysts, the reported system showed higher selectivity and lower Pd leaching.