Catalytic transfer hydrogenation has emerged as a pivotal chemical process with transformative potential in various industries. This review highlights the significance of catalytic transfer hydrogenation, a reaction that facilitates the transfer of hydrogen from one molecule to another, using a distinct molecule as the hydrogen source in the presence of a catalyst. Unlike conventional direct hydrogenation, catalytic transfer hydrogenation offers numerous advantages, such as enhanced safety, cost-effective hydrogen donors, byproduct recyclability, catalyst accessibility, and the potential for catalytic asymmetric transfer hydrogenation, particularly with chiral ligands. Moreover, the diverse range of hydrogen donor molecules utilized in this reaction have been explored, shedding light on their unique properties and their impact on catalytic systems and the mechanism elucidation of some reactions. Alcohols such as methanol and isopropanol are prominent hydrogen donors, demonstrating remarkable efficacy in various reductions. Formic acid offers irreversible hydrogenation, preventing the occurrence of reverse reactions, and is extensively utilized in chiral compound synthesis. Unconventional donors such as 1,4-cyclohexadiene and glycerol have shown a good efficiency in reducing unsaturated compounds, with glycerol additionally serving as a green solvent in some transformations. The compatibility of these donors with various catalysts, substrates, and reaction conditions were all discussed. Furthermore, this paper outlines future trends which include the utilization of biomass-derived hydrogen donors, the exploration of hydrogen storage materials such as metal-organic frameworks (MOFs), catalyst development for enhanced activity and recyclability, and the utilization of eco-friendly solvents such as glycerol and ionic liquids. Innovative heating methods, diverse base materials, and continued research into catalyst-hydrogen donor interactions are aimed to shape the future of catalytic transfer hydrogenation, enhancing its selectivity and efficiency across various industries and applications.

The escalating threats of climate change, pollution, and a rapidly growing global population are putting immense pressure on water resources, highlighting the urgent need for innovative wastewater recycling solutions. This study explores the potential of biochar, derived from common kitchen waste as a sustainable and efficient adsorbent for copper removal from contaminated water. Seven factors were studied for their influence on the adsorption process, including heavy metal concentration (50–250 ppm), biochar dosage (0.5–2.5 g), contact time (30 min to 29 h), temperature (20–80 °C), pH (2.67–8.07), and the efficacy of activated versus non-activated biochar, with activation carried out using phosphoric acid, silver nitrate, and sulfuric acid. Biochar characterization using Raman spectroscopy, specific surface area by Brunauer–Emmett–Teller analysis (BET), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy—Energy Dispersive X-ray Spectroscopy (SEM-EDX), and zeta potential analysis revealed its robust adsorption capacity. Notably, silver nitrate-loaded biochar exhibited the highest adsorption capacity (24.44 mg/g) at 250 ppm of copper and the highest removal rate at about 99.3%, whereas phosphoric acid activation reduced this capacity to 5 mg/g due to structural damage. Importantly, biochar’s adsorption capacity was found to be pH-independent, simplifying operational requirements for treatment systems. Optimal conditions for maximum copper removal were determined to be 100 ppm of copper, a temperature of 60 °C, and a contact time of 30 min. The Langmuir isotherm model best described the adsorption process, indicating a monolayer adsorption with a maximum capacity of 23.25 mg/g. This comprehensive analysis underscores biochar’s potential as a cost-effective, efficient, and environmentally friendly solution for copper removal from wastewater.

Catalytic transfer hydrogenation (CTH) provides a practical and sustainable approach for reducing unsaturated compounds, serving as an alternative to high-pressure H₂ in laboratory and fine chemical contexts. This broad reaction class includes asymmetric transfer hydrogenation (ATH), a key strategy in enantioselective synthesis due to its operational simplicity, high stereocontrol, and compatibility with sensitive functional groups. A central variable governing CTH efficiency is the role of bases, which may function as essential activators, co-hydrogen donors, or be entirely absent depending on the catalytic system. This review provides a comparison of base-assisted, base-free, and base-as-co-hydrogen-donor CTH methodologies across diverse metal catalysts and substrates. We highlight how bases such as triethylamine, K₂CO₃, and NaOH facilitate catalyst activation, modulate hydride formation, and tune reactivity and selectivity. The dual function of bases in formic-acid-driven systems is examined alongside synergistic effects observed with mixed-base additives. In contrast, base-free CTH platforms demonstrate how tailored ligand frameworks, metal-ligand cooperativity, and engineered surface basicity can eliminate the need for external additives while maintaining high activity. Through mechanistic analysis and cross-system comparison, this review identifies the key structural, electronic, and environmental factors that differentiate base-assisted from base-free pathways. Emerging trends—including greener hydrogen donors, advanced catalyst architectures, and additive-minimized protocols—are discussed to guide future development of sustainable CTH processes.