The development of economic and recyclable adsorbents for removing pollutants from contaminated water is gaining increasing attention. Agro residue or nature-based material sourced absorbents could revolutionize the future of wastewater treatment. Hence in this study, nanocellulose was synthesized from coconut husk fiber and immobilized onto chitosan to form hydrogel beads. The BET surface area and zeta potential of the adsorbent nanocrystalline cellulose–chitosan hydrogel (NCC–CH) bead was 25.77 m² g⁻¹ and +50.6 mV, respectively. The functional group analysis also confirmed that the adsorbent had functional groups appropriate for the adsorption of textile dyes. The adsorption performance of NCC–CH and also the influence of initial dye concentration, adsorbent dose, pH, and contact time was evaluated by batch adsorption studies with crystal violet (CV) and methylene blue (MB) dyes. The most favorable operational conditions achieved through I-optimal design in response surface methodology were 0.5 g NCC–CH, 1 h, 9 pH, and 60 mg L⁻¹ for CV removal (94.75%) and 0.13 g NCC–CH, 1 h, 9 pH, and 30 mg L⁻¹ for MB removal (95.88%). The polynomial quadratic model fits the experimental data with an R² value of 0.99 and 0.98 for CV and MB removal, respectively. The optimum depiction of the isotherm data was obtained using the Freundlich model for MB adsorption and Freundlich and Langmuir model for CV adsorption. The Dubinin–Radushkevich (D–R) isotherm was also a good fit to the adsorption of CV and MB dye, suggesting the physisorption due to its free energy of adsorption < 8 kJ mol⁻¹. The kinetics were effectively explained by a pseudo-second order model for both the dyes suggesting that chemical mechanisms influenced the adsorption of CV and MB dyes onto NCC–CH. The intraparticle diffusion model best suited the MB adsorption with three stages rather than the CV with a single step process. Also, the removal efficiency of adsorbent was retained at above 60% even after seven adsorption–desorption cycles indicating the effectiveness of the NCC–CH hydrogel beads for the removal of textile dyes.

The coconut-based agricultural wastes have gained wide attention as an alternative adsorbent for the removal of diverse pollutants from the industrial effluents. This paper presents the zinc chloride activation of adsorbent carbon and the utilization as an adsorbent for the removal of malachite green dye from aqueous solution. The characterisation of activated carbon was performed to get an insight into the adsorption mechanism. The ZnCl2 activated carbon acquired a higher specific surface area (544.66 m2 g−1) and stability (−32.6 mV). The impact of process parameters including contact time (20–220 min) and initial dye concentration (20–80 mg L−1) were evaluated on the effectiveness of activated carbon for dye removal. The results concluded that zinc chloride activated carbon showed a significant dye adsorption (39.683 mg g−1) at an initial concentration of 20 mg L−1 after 3 hours. Based on the correlation coefficient (R2), the Freundlich isotherm model (0.978–0.998) was best fitted for the experimental data followed by the intraparticle diffusion model (0.88–0.929) as the most appropriate model for malachite green dye removal. Additionally, the energy and thermogravimetric analysis portrayed the suitability of the carbon material to be used as an energy alternative to coal.

Activated carbon produced from coconut shells has been gaining interest in wastewater treatment as a potential carbon source for adsorption with desired porosity, surface area, and stability requirements. Acid activation has been preferred for activated carbon production due to its superiority over adsorption of malachite green dye. This study involved in the acid activation of coconut shell derived carbon and its characterisation was performed to study the surface functionalities, thermal stability, textural and structural morphologies. The activated carbon was used for the adsorption of malachite green dye from aqueous solutions and with a special insight by varying contact time (20–220 min) and initial dye concentration (20–80 mg L⁻¹) for adsorption study. Phosphoric acid-activated carbon has shown maximum adsorption capacity (X_m) of 32.787 mg g⁻¹ at initial malachite dye concentration of 20 mg L⁻¹ after 3 hours. All the adsorbents followed Freundlich isotherm with intra particle diffusion model as the rate-limiting step.

Aerosol black carbon (BC) mass concentrations were continuously monitored over a period of 2 years (April 2010 to May 2012) from a high-altitude location Ooty in the Nilgiris Mountain range in southern India to characterize the distinct nature of absorbing aerosols and their seasonality. Despite being remote and sparsely inhabited, BC concentrations showed significant seasonality with higher values (~ 0.96 ± 0.35 μg m−3) in summer (March to May), attributed to increased vertical transport of effluents in the upwind valley regions, which might have been confined to the surrounding valley regions within the very shallow winter boundary layer. The local atmospheric boundary layer (ABL) influence in summer was further modulated by the long-range transported aerosols from the eastern locations of Ooty. During monsoon (June–August), the concentrations were far reduced (~ 0.23 ± 0.06 μg m−3) due to intense precipitation. Diurnal variations were found conspicuous mainly during summer season associated with local ABL. The spectral absorption coefficients (αabs) depicted, in general, flatter distribution (mostly < 1.0 for more than 85% of daily mean values), suggesting the relative dominance of fossil fuel combustion, though showed marginal seasonal change with higher values of αabs in summer.

An experiment was conducted at Woodhouse farm, Horticultural Research Station, Ooty, during October 2017 to March 2018 to quantify the impact of elevated ozone and ozone protectant spray on plant growth, nutrients, biochemical and yield properties of turnip crop. The experiment was laid out in a factorial completely randomized block design and was replicated thrice. Elevated ozone exposure on turnip significantly reduced the plant height, tuber size, tuber weight, chlorophyll ‘a,’ chlorophyll ‘b’ and total chlorophyll content as well as the nutrient content of plant, viz., total nitrogen, total potassium, total manganese, iron, zinc and copper, also affected. Elevated ozone exposure significantly increased the antioxidant enzyme activity like catalase and peroxidase activity in addition to increment in total phosphorus content in leaf tissues. However, ozone protectants played a major role in nullifying the tropospheric ozone effect on growth and development, physiological traits and yield of turnip while tested with panchagavya performed better followed by neem oil and ascorbic acid.