Photocatalysis: an effective tool for photodegradation of dyes-a review

The disposal of dye-contaminated wastewater is a major concern around the world for which a variety of techniques are used for its treatment. The photocatalytic treatment of dye-contaminated wastewater is one of the treatment methods. Semiconductor-assisted photocatalytic treatment of dye-contaminated wastewater has gained pronounced attention recently. This review outlines the recent advancements in the photocatalytic treatment of dye-contaminated wastewater. The photocatalytic degradation of dyes follows three types of mechanisms: (1) dye sensitization through charge injection, (2) indirect dye degradation through oxidation/reduction, and (3) direct photolysis of dye. Several experimental parameters like initial concentration of dyes, pH, and catalyst dosage significantly affect the photocatalytic degradation of dyes. The photocatalytic materials can be categorized into three generations. The single-component (e.g., ZnO, TiO₂) and multiple component semiconductor metal oxides (e.g., ZnO-TiO₂, Bi₂O₃-ZnO) are categorized as first-generation and second-generation photocatalysts, respectively. The photocatalysts dispersed on an inert solid substrate (e.g., Ag-Al₂O₃, ZnO-C) are classified as third-generation photocatalysts. Finally, we reviewed the challenges that affect the photocatalytic degradation of dyes.

Modern Catalysts in A3- Coupling Reactions

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Propargylamines are an important constituent of diverse, biologically active and industrially valuable compounds. These useful, convenient and effective compounds can be synthesized via the A3-coupling reactions between an aldehyde, amine, and alkyne in the presence of a catalyst. In the past years, most of the catalysts containing transition metals were applied in these reactions, but today, various heterogeneous catalysts, especially nanocatalysts are used. The purpose of this review was to introduce some modern catalysts for the A3-coupling reaction.

Two inorganic–organic hybrid silver-polyoxometalates as reusable catalysts for one-pot synthesis of propargylamines via a three-component coupling reaction at room temperature

Two silver-polyoxometalates [Ag₃L₂(DMSO)₂][PW₁₂O₄₀]·4DMSO (1) and [(Ag₂L₂)₂][SiW₁₂O₄₀]·10DMSO·2H₂O (2) are made and 1 shows good catalytic activities for three-component coupling reaction.

CuI incorporated cobalt ferrite nanoparticles as a magnetically separable catalyst for oxidative amidation reaction

A Cu-incorporated magnetic nanocatalyst has been developed for oxidative amidation of aryl aldehydes with 2-aminopyridine in the presence of TBHP.

Highly Efficient, Low-Cost, and Magnetically Recoverable FePt⁻Ag Nanocatalysts: Towards Green Reduction of Organic Dyes

Nowadays, synthetic organic dyes and pigments discharged from numerous industries are causing unprecedentedly severe water environmental pollution, and conventional water treatment processes are hindered due to the corresponding sophisticated aromatic structures, hydrophilic nature, and high stability against light, temperature, etc. Herein, we report an efficient fabrication strategy to develop a new type of highly efficient, low-cost, and magnetically recoverable nanocatalyst, i.e., FePt⁻Ag nanocomposites, for the reduction of methyl orange (MO) and rhodamine B (RhB), by a facile seed deposition process. X-ray diffraction results elaborate that the as-synthesized FePt⁻Ag nanocomposites are pure disordered face-centered cubic phase. Transmission electron microscopy studies demonstrate that the amount of Ag seeds deposited onto the surfaces of FePt nanocrystals increases when increasing the additive amount of silver colloids. The linear correlation of the MO and RhB concentration versus reaction time catalyzed by FePt⁻Ag nanocatalysts is in line with pseudo-first-order kinetics. The reduction rate constants of MO and RhB increase with the increase of the amount of Ag seeds. FePt⁻Ag nanocomposites show good separation ability and reusability, and could be repeatedly applied for nearly complete reduction of MO and RhB for at least six successive cycles. Such cost-effective and recyclable nanocatalysts provide a new material family for use in environmental protection applications.

A facile synthesis methodology for preparation of Ag–Ni-reduced graphene oxide: a magnetically separable versatile nanocatalyst for multiple organic reactions and density functional study of its electronic structures

Here, we report a simple ‘in situ’ co-precipitation reduction synthesis method for the preparation of nanocatalysts composed of Ag, Ni nanoparticles, and reduced graphene oxide (RGO). First-principles calculations based on Density Functional Theory (DFT) were performed to obtain the electronic structures and properties of Ag–Ni-graphene superlattice and to understand the interfacial interactions which exist at the interface between Ag, Ni, and graphene. The catalytic performance of the synthesized catalysts (Ag_xNi_(1−x))_yRGO_(100−y) were evaluated for four reactions (i) reduction of 4-nitrophenol (4-NP) in the presence of excess NaBH₄ in aqueous medium, (ii) A3 coupling reaction for the synthesis of propargylamines, (iii) epoxidation of styrene, and (iv) ‘Click reaction’ for the synthesis of 1,2,3-triazole derivatives. For all of these reactions the catalyst composed of Ag, Ni, and RGO, exhibited significantly higher catalytic activity than that of pure Ag, Ni, and RGO. Moreover, an easy magnetic recovery of this catalyst from the reaction mixture after completion of the catalytic reactions and the good reusability of the recovered catalyst is also reported here. To the best of our knowledge, this is the first time the demonstration of the versatile catalytic activity of (Ag_xNi_(1−x))_yRGO_(100−y) towards multiple reactions, and the DFT study of its electronic structure have been reported.

Here, we report a simple ‘in situ’ co-precipitation reduction synthesis method for the preparation of nanocatalysts composed of Ag, Ni nanoparticles, and reduced graphene oxide (RGO).