Some chemical substances could improve the sorption capacity of biochars. In this paper, sodium humate was introduced to the pyrolysis of two biomass samples at 600 °C, and sodium humate–biochars have been successfully synthesized. The surface area and surface morphologies of all of the biochars were characterized, and the results indicated that sodium humate–biochars have higher surface areas, and sodium humate particles were grown on the surfaces of the biochars. Adsorption isotherm and kinetics of methylene blue (MB) onto the biochars were carried out by batch adsorption experiments. The results suggested that incorporation of sodium humate could increase the adsorption capacity of MB onto the biochars (from 10.79 to 16.21, 8.62 to 11.03 mg/g for peanut shells and white clover residues, respectively). The adsorption experimental results also suggest that the adsorption process of MB onto sodium humate–biochars is controlled by both intraparticle diffusion and film diffusion. As a whole, this work probes the possibility of sodium humate to modify the surface of biochar and improve its adsorption ability with contaminants.

Mine fires are one of the primary natural disasters in coal production. The majority of mine fires are caused by the spontaneous combustion of coal. To reduce the risk of spontaneous combustion of coal, a new fire prevention and extinguishing hydrogel has been developed. Poly(acrylic acid-co-methacrylamide) (P(AA-co-MAA)) and chitosan-grafted poly(acrylic acid-co-methacrylamide) (CTS-g-P(AA-co-MAA)) were prepared by aqueous solution polymerization, and their characteristics have been studied by scanning electron microscopy and Fourier transform infrared spectroscopy. The swelling ability and water retention of the hydrogels were also tested and compared. The experimental results showed that the grafting of chitosan can improve the water-absorbing ability of the hydrogel in acidic solution and deionized water and enhance the water retention of the hydrogel. The thermogravimetric experiments of the mixture of the hydrogel and coal showed that the thermal stability of the mixture was the best when the ratio of hydrogel to coal was 1:10, and the grafting of chitosan did not weaken the thermal stability of the hydrogel. In addition, the thermogravimetry and differential scanning calorimetry measurement of coal with the hydrogel in air proved that the CTS-g-P(AA-co-MAA) hydrogel effectively prevented the initial oxidation of coal. Thus, CTS-g-P(AA-co-MAA) is recommended as an inhibitor in preventing coal oxidation.

Biofuels produced via thermochemical conversions of waste biomass could be sustainable alternatives to fossil fuels but currently require costly downstream upgrading to be used in existing infrastructure. In this work, we explore how a low-cost, abundant clay mineral, bentonite, could serve as an in situ heterogeneous catalyst for two different thermochemical conversion processes: pyrolysis and hydrothermal carbonization (HTC). Avocado pits were combined with 20 wt% bentonite clay and were pyrolyzed at 600 °C and hydrothermally carbonized at 250 °C, commonly used conditions across the literature. During pyrolysis, bentonite clay promoted Diels–Alder reactions that transformed furans to aromatic compounds, which decreased the bio-oil oxygen content and produced a fuel closer to being suitable for existing infrastructure. The HTC bio-oil without the clay catalyst contained 100% furans, mainly 5-methylfurfural, but in the presence of the clay, approximately 25% of the bio-oil was transformed to 2-methyl-2-cyclopentenone, thereby adding two hydrogen atoms and removing one oxygen. The use of clay in both processes decreased the relative oxygen content of the bio-oils. Proximate analysis of the resulting chars showed an increase in fixed carbon (FC) and a decrease in volatile matter (VM) with clay inclusion. By containing more FC, the HTC-derived char may be more stable than pyrolysis-derived char for environmental applications. The addition of bentonite clay to both processes did not produce significantly different bio-oil yields, such that by adding a clay catalyst, a more valuable bio-oil was produced without reducing the amount of bio-oil recovered.