Cobalt-lignosulfonate complex derived non-noble catalysts: Facile valorization for high-performance redox conversion of organic pollutants

A versatile and scalable preparation of hierarchically porous and highly active catalysts from a lignosulfonate biopolymer was proposed. The materials were systematically evaluated for catalytic oxidation of metformin, sulfamethoxazole, and phenol and reductive hydrogenation of 4-nitrophenol and 1-nitronaphthalene as model pharmaceutical and industrial pollutants. Temperature, background matrix, substrate, catalyst and chemical loading govern the conversion rates differently. Complete phenol and sulfamethoxazole removals were achieved in 90 min at very low dosage of Oxone® (0.325 mM) and catalyst (0.05 g/L) while mineralizing more than 80% (phenol and sulfamethoxazole) and 36% (metformin). Humic acid, gallic acid, sodium azide, chloride and bicarbonate ions at environmentally relevant levels possessed minor inhibitory effects on sulfamethoxazole degradation. Results from EPR spin-trapping, radical quenching, and D₂O exchange experiments support a dual-mode activation mechanism of Oxone®. In the catalytic reduction of the nitro compounds, excellent turnover frequencies of up to 3.75 × 10⁻²/min for 4-nitrophenol and 2.04 × 10⁻³/min for 4-nitronaphthalene were attained, outperforming the capacity of many previously reported catalysts. Furthermore, various solvent exchange studies reveal the significant role of structured surficial moieties in a “water assisted” catalytic mechanism and reduction pathway. The N, S co-doped samples exhibited superior performance, synergistically attributable to the active heteroatoms and Co-N_x/S_y-C clusters on porous sp²-conjugated framework. For both processes, the catalysts maintained their magnetic responsiveness, high activity and stability profile for at least five cycles, highlighting the practical applicability of this benign valorization route and the envisaged straightforward heterogeneous applications.