Bagasse heavy ash-derived Zn-loaded porous silica with tunable mesopores: Effect of monomodal and bimodal pores on VOCs adsorption

•Bagasse heavy ash-derived bimodal mesoporous silica (BPS) products were prepared.•An environmentally-friendly, single–template pH alteration process was applied.•Hydrolysis–condensation rate alteration facilitates formation of tunable mesopores.•Methanol and benzene adsorption capacities of BPS were 4.10 and 7.51 times greater than monomodal MPS.•Environmental impact in terms of global warming and marine ecotoxicity has been improved by 1.20 and 1.54 times compared to conventional synthesis (TEOS).