Nanotechnology is rapidly sweeping through all the vital fields of science and technology such as electronics, aerospace, defense, medicine, and catalysis. It involves the design, synthesis, characterization, and applications of materials and devices on the nanometer scale. At the nanoscale, physical and chemical properties differ from the properties of the individual atoms and molecules of bulk matter. In particular, the design and development of silica nanomaterials have captivated the attention of several researchers worldwide. The applications of hybrid silicas are still limited by the lack of control on the morphology and particle size. The ability to control both the size and morphology of the materials and to obtain nano-sized silica particles has broadened the spectrum of applications of mesoporous organosilicas and/or has improved their performances. On the other hand, adsorption is a widely used technique for the separation and removal of pollutants (metal ions, dyes, organics,...) from wastewater. Silica nanoparticles have specific advantages over other materials for adsorption applications due to their unique structural characteristics: a stable structure, a high specific surface area, an adjustable pore structure, the presence of silanol groups on the surface which allow easy modification, less environmental harm, simple synthesis, low cost, etc. Silica nanoparticles are potential adsorbents for pollutants. We present herein an overview of the different types of silica nanoparticles going from the definitions to properties, synthetic approaches and the mention of potential applications. We focus mainly on the recent advances in the adsorption of different target substances (metal ions, dyes and other organics).

Photocatalytic degradation technology has received much attention from researchers in the last few decades, due to its easy and cost-effective nature. A lot of review articles have been published on dyes via photocatalytic degradation, but most of the review articles lack a detailed and in-depth photocatalytic degradation mechanism of dyes. Numerous review articles are available on photocatalysis. Here, in this review article, we are mainly focused on the complete and in-depth photocatalytic degradation mechanism of four commonly used dyes such as Malachite Green, Methylene Blue, Congo Red and Rhodamine B, which will be highly useful for the new researchers that work on dyes’ photocatalytic degradation. Initially, various aspects of dyes have been included in this review article, comprehensively. The main focus was on the covalent organic framework-based photocatalysts for dyes’ photocatalytic degradation, due to their porous nature and various unique properties. Various synthesis routes and the photocatalytic performance of covalent organic frameworks and composite of covalent organic frameworks have been highlighted in this review article. In the last section of this review article, the main stimulus was the four mentioned dyes’ properties, uses, and toxicity, and the photocatalytic degradation mechanism through various paths into environmentally friendly and less-harmful compounds in the presence of photocatalysts. Factors effecting the photocatalytic degradation, economic cost, challenges and future aspects of photocatalytic technology were also included in this review article. This review article will be highly useful for those researchers that work on the photocatalytic degradation of various dyes and search for the complete degradation of complex dye molecules.

The palladium-catalysed allylic substitution reaction is one of the most important reactions in transition-metal catalysis and has been well-studied in the past decades. Most of the reactions proceed through an outer-sphere mechanism, affording linear products when monosubstituted allyl reagents are used. Here, we report an efficient Palladium-catalysed protocol for reactions of β-substituted ketones with monosubstituted allyl substrates, simply by using N-heterocyclic carbene as ligand, leading to branched products with up to three contiguous stereocentres in a (syn, anti)-mode with excellent regio and diastereoselectivities. The scope of the protocol in organic synthesis has been examined preliminarily. Mechanistic studies by both experiments and density functional theory (DFT) calculations reveal that the reaction proceeds via an inner-sphere mechanism—nucleophilic attack of enolate oxygen on Palladium followed by C–C bond-forming [3,3’]-reductive elimination.

A method to selectively capture and separate gold from secondary resources is urgently needed to offset the increasing depletion of gold resources, and to meet the sustainable supply of precious metal resources and to reduce the environmental impact from toxic metals. Unfortunately, the lack of viable recycling techniques in developing countries results in extremely low precious metal recovery rates. In this work, highly selective and redox active adsorbent-thiourea functionalised magnetic core stirring rods (MCSR-ATU) were prepared for use in the recycling of gold in actual e-waste. Benefiting from the stirring motion of the rotating magnetic field, the MCSR-ATU exhibits an enhanced adsorption capacity and kinetics, reaching the maximum adsorption capacity (224.97 mg g⁻¹) for Au(III) at 30 min at a pH of 3.0 at 313 K. The adsorption process follows the pseudo-second order model and the Langmuir model. The distribution coefficient (K_d = 405 500 mL g⁻¹), the selection coefficient (αAu³⁺/Mⁿ⁺ = >8730) and the concentration coefficient (CF = 997.54 mL g⁻¹) reveal the remarkable selectivity of the MCSR-ATU for Au(III), which is mainly attributed to the strong Lewis soft-soft interaction and the redox reaction between Au(III) and the S-containing groups. Furthermore, the MCSR-ATU demonstrated excellent selectivity with a 94.66% gold capture rate even in actual samples, showing great potential for recycling gold from complex e-waste leaching solution with a low concentration of gold and a high level of interfering cations. It should be mentioned that the redox-active thiourea groups can convert, in situ, the captured Au(III) directly into Au(0), which can then be used for hydrogenation of 4-nitrophenol with excellent catalytic activity (the rate constant k = 2.394 min⁻¹) and reusability. This work provides a sustainable and circular strategy for the disposal of e-waste.