Moringa oleifera (MO) seed coat, a postharvest waste of MO seed, was mercerized and used as eco-friendly adsorbent for removal of Congo red (CR) dye from aqueous solution at different time and temperature. Mercerized M. oleifera seed coat (MSC) was characterized through scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) before and after adsorption process. Data obtained from effect of contact time on CR dye-uptake were applied on Elovich, pseudo-first- and second-order kinetic models, as well as on intraparticle diffusion and Boyd models. SEM and FTIR showed adsorption of CR dye on MSC through filled holes (SEM), appearance of new and shifting existing of functional groups (FTIR) on the surface of MSC after adsorption process. Adsorption kinetics was seen to be best fitted with pseudo-second-order model with the highest value of correlation coefficient at all temperatures. Film diffusion mechanism controlled the adsorption process, where external mass transfer was higher than internal mass transfer. Adsorption kinetics parameters confirmed removal of CR dye from aqueous solution through chemical and physical adsorption on MSC.

Chemically activated cocoa leaves biochar (CLB) was successfully prepared from fallen cocoa leaves (CLs) via ZnCl₂-activation and pyrolysis at 700 °C for sequestration of toxic crystal violet (CV) dye from aqueous solution. CLs and CLB were characterized using elemental analysis (CHN/O), Brunauer-Emmett-Teller method (BET), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), X-ray diffraction (XRD) spectroscopy and scanning electron microscopy (SEM). The optimum conditions for effective removal of CV dye from aqueous solution (75.67% for CLs and 99.87% for CLB) were pH 9, initial CV dye concentration 100 mg/L, adsorbent (CLs/CLB) dose 0.4 g/L, contact time 160 min and temperature 300 K. Modified Ritchie second order best described kinetic and Liu model described equilibrium adsorption. CLs and CLB with maximum adsorption capacities 190.70 and 253.3 mg/g respectively, compete favorably with adsorbents used for removal of CV dye from wastewater in the literature. The high BET surface area (957.02 m²/g) and mean pore diameter (7.21 nm) were indicators of better adsorption efficiency of CLB. CLs showed adsorption to proceed towards endothermic process, while it was exothermic process for CLB. This study established the suitability of cocoa leaves as sustainable and environmental friendly precursor for preparation of adsorbent for the treatment of dye-containing wastewater.

Bridelia ferruginea B dye was extracted from the bark of the tree using aqueous extraction method. Extracted dye was used to dye cellulosic (cotton) fabric in presence of 5% calcium chloride (CaCl₂) or 5% alum (KAl(SO₄)₂·12H₂O) of weight of fabric (o.w.f) as mordant. Fabric dyed without mordant was lighter in hue than metal ion mordanted dyed fabrics. The fabrics dyed in presence of calcium chloride as mordant are of deeper hue than those dyed with alum as mordant. Hence, their dye-uptake and color strength (K/S) are in the same order. K/S value of fabric dyed with alum is 43.71% higher than that without mordant and fabric dyed with calcium chloride has K/S value 51.09% higher than dyed with alum as mordant. CIEL*a*b* coordinate indicator and color space quadrant showed that those dyed fabrics without mordant and with alum as mordant are closer to yellow than red color. Those cellulosic fabrics dyed with calcium chloride as mordant are closer to red than yellow color as confirmed in colour space quadrant. Pre-mordanted dyed fabrics are of deeper color than post-mordanted dyed fabrics than meta-mordanted dyed fabrics than unmordant dyed fabric. Fastness properties of B. ferruginea B dyed cellulosic fabrics ranged from good (3) to excellent (5).