Zakir Hossain

The increasing environmental concerns regarding the depletion of fossil resources and the excessive production of waste have shifted attention toward sustainable materials derived from renewable resources. Biobased activated carbon (BAC), derived from biomass, has emerged as a promising alternative to conventional fossil-derived activated carbon (AC), offering numerous advantages in terms of sustainability, cost-effectiveness, environmental impact, and wide-ranging applications. The production process of BAC involves the carbonization of biomass materials followed by activation, which enhances its porosity and surface area. These characteristics make BAC highly effective for applications in water and air purification, energy storage, and environmental remediation. In water treatment, BAC is used to remove pollutants like heavy metals, organic contaminants, and microplastics through adsorption. In air purification, it helps eliminate harmful gases and volatile organic compounds (VOCs). Additionally, BAC has emerged as a key material in energy storage technologies, particularly in supercapacitors, due to its high surface area and electrical conductivity. Its use in soil amendment and environmental remediation is also gaining attention for removing toxic substances from contaminated environments. The development of BAC is aligned with global efforts to reduce carbon footprints and promote circular economies. Its versatility and sustainability make BAC a promising material in addressing environmental challenges while providing an alternative to fossil fuel-derived products. This chapter will cover all the possible applications where BAC is being used.

The kinetics of total organic carbon (TOC) destruction during supercritical water gasification (SCWG) of glucose were studied at 400–500°C and 25 MPa in a 600 mL batch reactor. Both TOC and water concentrations are critical for the conversion of TOC in supercritical water, especially at longer residence times. Initially, it was assumed that the TOC destruction reaction followed first‐order kinetics ignoring the water concentration. However, experimental results showed that the feed‐to‐water ratio had a significant effect on TOC decomposition. Considering the water concentration in the reaction, the reaction orders of TOC (2.35) and water (1.45) were calculated using nonlinear regression analysis (the Runge‐Kutta method). The estimated pre‐exponential factor (k’) and activation energy (E) were calculated to be 8.1 ± 2/min and 90.37 ± 9.38 kJ/mol respectively.

In this study, we report a single-step continuous production of straight-chain liquid hydrocarbons from oleic acid and other fatty acid derivatives of interest including castor oil, frying oil, and palm oil using Mo, MgO, and Ni on Al₂O₃ as catalysts in subcritical water. Straight-chain hydrocarbons were obtained via decarboxylation and hydrogenation reactions with no added hydrogen. Mo/Al₂O₃ catalyst was found to exhibit a higher degree of decarboxylation (92%) and liquid yield (71%) compared to the other two examined catalysts (MgO/Al₂O₃, Ni/Al₂O₃) at the maximized conditions of 375 °C, 4 h of space time, and a volume ratio of 5:1 of water to oleic acid. The obtained liquid product has a similar density (0.85 kg/m³ at 15.6 °C) and high heating value (44.7 MJ/kg) as commercial fuels including kerosene (0.78–0.82 kg/m³ and 46.2 MJ/kg), jet fuel (0.78–0.84 kg/m³ and 43.5 MJ/kg), and diesel fuel (0.80–0.96 kg/m³ and 44.8 MJ/kg). The reaction conditions including temperature, volume ratio of water-to-feed, and space time were maximized for the Mo/Al₂O₃ catalyst. Characterization of the spent catalysts showed that a significant amount of amorphous carbon deposited on the catalyst could be removed by simple carbon burning in air with the catalyst recycled and reused.

Synthesis of activated carbon from waste biomass is of current interest towards sustainability. The properties of biomass-derived activated carbon largely depend on the carbonization process. This study reports the preparation of mesoporous activated carbon with extremely high surface area from hemp bast fiber using hydrothermal processing. Hot water processing (390–500 °C) followed by activation using KOH and NaOH was investigated at different mass ratios. The described approach was found to enhance the mesoporosity (centered at 3.0 to 4.5 nm) of the hemp-derived activated carbon (HAC) from activation [confirmed by BJH (Barrett-Joyner-Halenda) pore size distribution and TEM (transmission electron microscopy) imaging]. BET (Brunauer-Emmett-Teller) results showed that the product has an extremely high surface area (2425 m²/g) while the surface functional groups (–OH, –COOH, C=C/C–C) were confirmed by FTIR (Fourier transform infrared spectroscopy) and further quantified by XPS (X-ray photoelectron spectroscopy). Increasing KOH concentration was found to enhance the surface area with a maximum biochar-to-KOH (g/g) ratio of 1:3. The crystallite domain size of HAC was determined using Raman spectroscopy of different wavelengths. The procedure described in this study is an environmentally friendly scalable route for the mass production of activated carbon using hemp fiber.

Synthesis of activated carbon from waste biomass is of current interest towards sustainability. The properties of biomass derived activated carbon largely depends on the carbonization process. This study reports preparing extremel high surface area mesoporous activated carbon from hemp bast fibre using hydrothermal processing. Processing in hot water (390-500oC), then activation using KOH and NaOH was investigated at different loading ratios. The described approach was found to enhance the mesoporosity (centered at 3.0 to 4.5 nm) of the hemp derived activated carbon (HAC) from activation (confirmed by BJH pore size distribution and TEM imaging). BET results showed that the product has an extremely high surface area (2425 m2/g) while the surface functional groups (-OH, COOH, C=C/C-C) were confirmed and quantified by XPS and FTIR results. Increasing KOH concentration was found to enhance the surface area with an optimum biochar to KOH ratio of 1:3. The crystallite domain size of HAC was determined using Raman spectroscopy of different wavelengths. The procedure described in this study is an environmentally friendly scalable route for the mass production of activated carbon using hemp fiber.

Catalytic hydrothermal conversion of non‐edible corn distillers oil (CDO), a low‐value by‐product of the ethanol industries, into high value fuel‐grade hydrocarbons was investigated in near‐supercritical water. The decarboxylation experiments were conducted using activated carbon in a 300 mL batch stirred tank reactor at reaction temperatures of 300–400 °C with pressure ranges from 2200–2500 psi (≈15–17 MPa), water/CDO (v/v) ratios of 2:1 to 5:1, and reaction times of 0.5 to 4 h at constant stirring speed (800 rpm). For the first time, complete removal of the −COO− group from CDO was achieved at 400 °C with 4 h of reaction time and a water/CDO (v/v) ratio of 4:1. The liquid products obtained were a mixture of saturated hydrocarbons, mainly C₈–C₁₆ (selectivity 49.7 %) and heptadecane (48.9 %) which have similar specific gravity, higher heating value (HHV), cloud points, and pour points to those of commercial fuels. 65 % liquid yield was obtained under optimal reaction conditions. The reaction mechanism was found to follow pseudo‐first‐order kinetics with an activation energy 66.1±3 kJ mol⁻¹, which is much lower than similar reported literature values for the decarboxylation process.