Cotton stalk-derived hydrothermal carbon for methylene blue dye removal: investigation of the raw material plant tissues

Unlocking the potential of cotton stalk as a renewable source of cellulose: A review on advancements and emerging applications

Cotton stalk (CS) is a global agricultural residue, with an annual production of approximately 50 million tons, albeit with limited economic significance. The utilization of cellulose derived from CS has gained significant attention in green nanomaterial technologies. This interest stems from its unique properties, including biocompatibility, low density, minimal thermal expansion, eco-friendliness, renewability, and its potential as an alternative source for chemicals, petroleum, and biofuels. In this review, we delve into various extraction and characterization methods, the physicochemical attributes, recent advancements, and the applications of cellulose extracted from CS. Notably, the steam explosion method has proven to yield the highest cellulose content (82 %) from CS. Moreover, diverse physicochemical properties of cellulose can be obtained through different extraction techniques. Sulfuric acid hydrolysis, for instance, yields nanocrystalline cellulose fibers measuring 10-100 nm in width and 100-850 nm in length. Conversely, the steam explosion method yields cellulose fibers with dimensions of 10.7 μm in width and 1.2 mm in length. CS-derived products, including biochar, aerogel, dye adsorbents, and reinforcement fillers, find applications in various industries, such as environmental remediation and biodegradable packaging. This is primarily due to their ready availability, cost-effectiveness, and sustainable nature.

Pristine wild sugarcane (Saccharum spontaneum) as a biosorbent for removal of methylene blue from wastewater: isotherm, kinetics and regeneration studies

Saccharum spontaneum, popularly known as Kashful (KF) is a seasonal perennial grass with thin culms, mostly an abundantly growing shrub during the autumn season in southern Asia. It is used as no-cost scavenger to convincingly arrest methylene blue, a recalcitrant dye from colored effluent. FTIR, FESEM-EDX, and BET surface area characterize the material well whereas the surface activity was evaluated from zero-point charge (pHZPC = 6.720). FTIR highlights the presence of polyphenolic and carboxylate moieties. The surface texture is rod-like with intermittent non-homogeneous pores with occasional fractures. The equilibrium reaches within 60 min with the maximum adsorption capacity of 20.917 mg/g. The fibrous powder of kashful stalk (KFS) follows pseudo-second-order (R2 = 0.999 for linear and R2 = 0.985 for non-linear) kinetics and both Langmuir and Freundlich isotherm model (for linear, Langmuir R2=0.995; for non-linear, R2 = 0.994 for both Langmuir and Freundlich model). The uptake process was spontaneous (ΔG= -3.077 kJ/mol) and endothermic (ΔH = 17.815 kJ/mol). 1:1 methanol could regenerate the dye-loaded material in up to 55% and onward efficiency was conducive for three consecutive cycles. Industrial effluent analysis suggests a real-time removal of ∼55% in the first cycle. Saccharum spontaneum could be exercised to solve environmental problems related to colored water.

Influence of hydrothermal carbonization conditions on the porosity, functionality, and sorption properties of microalgae hydrochars

Green microalgae is a possible feedstock for the production of biofuels, chemicals, food/feed, and medical products. Large-scale microalgae production requires large quantities of water and nutrients, directing the attention to wastewater as a cultivation medium. Wastewater-cultivated microalgae could via wet thermochemical conversion be valorised into products for e.g., water treatment. In this study, hydrothermal carbonization was used to process microalgae polycultures grown in municipal wastewater. The objective was to perform a systematic examination of how carbonization temperature, residence time, and initial pH affected solid yield, composition, and properties. Carbonization temperature, time and initial pH all had statistically significant effects on hydrochar properties, with temperature having the most pronounced effect; the surface area increased from 8.5 to 43.6 m2 g-1 as temperature was increased from 180 to 260 °C. However, hydrochars produced at low temperature and initially neutral pH generally had the highest capacity for methylene blue adsorption. DRIFTS analysis of the hydrochar revealed that the pH conditions changed the functional group composition, implying that adsorption was electrostatic interactions driven. This study concludes that un-activated hydrochars from wastewater grown microalgae produced at relatively low hydrothermal carbonization temperatures adsorb methylene blue, despite having low surface area.

Fe-modified fly ash/cotton stalk biochar composites for efficient removal of phosphate in water: mechanisms and green-reuse potential

Excessive phosphate content input into natural water can lead to the waste of resource and eutrophication. Biochar is a kind of low-cost adsorbent. However, its adsorption capacity for phosphate is low. In order to solve this problem, Fe compound-modified fly ash/cotton stalk biochar composites (Fe-FBC) were prepared through co-pyrolyzed fly ash and cotton stalk at 800℃, followed by infiltration of FeSO₄ solution. The samples were characterized by scanning electron microscopy, Brunauer-Emmett-Teller, X-ray diffraction, Fourier transform infrared spectroscopy, and zeta potential. After modification, the hydrophilicity and polarity of Fe-FBC increased. In addition, the pore volume, specific surface area, and surface functional groups were significantly improved. The adsorption behavior of Fe-FBC for the removal of phosphate from water can be well fitted by the pseudo-second-order kinetic and Sips isotherm adsorption model, with a maximum adsorption capacity of 47.91 mg/g. Fe-FBC maintained a high adsorption capacity in the pH range of 3-10. The coexisting anions (NO₃^-, SO₄^2-, and Cl^-) had negligible effects on phosphate adsorption. The adsorption mechanisms of Fe-FBC include electrostatic attraction, ligand exchange, surface complexation, ion exchange, chemical precipitation, and hydrogen bonding. Moreover, the desorption process of phosphate was investigated, indicating that the phosphate-saturated Fe-FBC could use as slow-release phosphate fertilizer. This study proposed a potentially environmental protection and recycling economy approach, which consists of recycling resources and treating wastes with wastes.

An overview of torrefied bioresource briquettes: quality-influencing parameters, enhancement through torrefaction and applications

In recent years, the need for clean, viable and sustainable source of alternative fuel is on the rampage in the global space due to the challenges posed by human factors including fossil induced emissions, fuel shortage and its ever-rising prices. These challenges are the major reason to utilize alternative source of energy such as lignocellulosic biomass as domestic and industrial feedstock. However, biomass in their raw form is problematic for application, hence, a dire need for torrefaction pre-treatment is required. The torrefaction option could ameliorate biomass limitations such as low heating value, high volatile matter, low bulk density, hygroscopic and combustion behaviour, low energy density and its fibrous nature. The torrefied product in powder form could cause air pollution and make utilization, handling, transportation, and storage challenging, hence, densification into product of higher density briquettes. This paper therefore provides an overview on the performance of torrefied briquettes from agricultural wastes. The review discusses biomass and their constituents, torrefaction pre-treatment, briquetting of torrefied biomass, the parameters influencing the quality, behaviour and applications of torrefied briquettes, and way forward in the briquetting sector in the developing world.

Microwave-Assisted Hydrothermal Carbonisation of Waste Biomass: The Effect of Process Conditions on Hydrochar Properties

Hydrochars are an alternative form of biochar produced by hydrothermal carbonisation (HTC), a potentially cheaper and greener method. In this paper, the effect of multiple variables on hydrochar properties was investigated. Waste biomass was converted to hydrochar via microwave-assisted hydrothermal carbonisation. The variables were temperature, solution ratio (water-biomass ratio), time, particle size, pH and acetone washing. The measured properties were yield, carbon, oxygen and ash content, higher heating value (HHV), carbon and energy recovery and dye and water adsorption. Feedstock significance was investigated using apple, wheat, barley, oat and pea straw. The investigation into this specific combination of variables and feedstock has not been done before. HTC increased carbon content (~60%), HHV (~24 MJ/kg) and water adsorption and reduced oxygen content and dye adsorption. Thermal analysis suggested hydrochars were not suitable for sequestration. Decreasing the solution ratio was the most significant factor in increasing yield, carbon recovery and energy yield. Increasing the temperature was the most significant factor in increasing carbon and decreasing oxygen content. This affected HHV, with higher temperatures producing a higher energy material, surpassing brown coal. Hydrochars produced at a high solution ratio, temperature and times showed the best carbonisation. Smaller particle size increased yield and carbonisation but increased ash content. Low solution pH increased carbon content, HHV and water adsorption but lowered yield, carbon recovery, energy yield, dye adsorption and oxygen and ash content. High pH increased ash content and dye adsorption but lowered yield, carbon recovery, energy yield and dye adsorption. Acetone decreased yield, carbon recovery, energy yield, carbon content and HHV but increased oxygen, ash content and dye and water adsorption. Barley biomass showed the highest yield and carbon recovery, and pea showed the highest energy yield and HHV. Apple showed the highest carbon content. All the hydrochars showed promise as solid fuels, a soil additive and a precursor for activated carbon but lacked high adsorption for pollutant adsorbents and stability for carbon sequestration.

Low Temperature One-Pot Hydrothermal Carbonization of Corn Straw into Hydrochar for Adsorbing Cadmium (II) in Wastewater

Corn straw, a typical agricultural waste, was directly converted into hydrochar with a yield of 77.56% by hydrothermal carbonization at 140–230 °C for 2 h with a solid–liquid ratio of 1:20. The morphology and surface properties were characterized by elemental analysis, specific surface area and pore size analysis and Fourier transform infrared spectroscopy. The results showed that with the increase of hydrothermal reaction temperature, some physical and chemical properties such as the increase of hydrocarbon content, crystallinity, and specific surface area of hydrochar changed significantly. A series of chemical reactions such as dehydration, decarboxylation, and aromatization occurred in the hydrothermal carbonization process so that the prepared hydrochar had rich oxygen-containing functional groups (-HO, C-O-C, C=O) and unique porous structure made the hydrochar prepared at 170 °C had the best removal effect on Cd2+ in solution (5.84 mg/g). These specific conditions could remove Cd2+ and greatly improve the adsorption performance. The pseudo-second-order kinetic model and Freundlich isotherm model could better describe the adsorption behavior of Cd2+. Therefore, corn straw hydrochar as a potential adsorbent for removing Cd2+ from water.

Rice husk hydrochars from metal chloride-assisted hydrothermal carbonization as biosorbents of organics from aqueous solution

Hydrochar a carbon-rich material resulting from hydrothermal carbonization of biomass, has received substantial attention because of its potential application in various areas such as carbon sequestration, bioenergy production and environmental amelioration. A series of hydrochars were prepared by metal chloride-assisted hydrothermal carbonization of rice husk and characterized by elemental analysis, zeta potential, X-ray diffraction, Brunauer-Emmett-Teller measurements, Fourier transform infrared spectroscopy, thermogravimetric analysis, X-ray photoelectron spectroscopy and scanning electron microscopy. The results reveal that the prepared hydrochars have carbon contents ranging from 45.01 to 58.71%, BET specific areas between 13.23 and 45.97 m2/g, and rich O-containing functional groups on the surfaces. The metal chlorides added in the feedwater could improve the degree of carbonization and show significant effects on the physical, chemical and adsorption properties of the hydrochars. The adsorption of the selected organics on the hydrochars is a spontaneous and physisorption-dominated process. The hydrochars possess larger adsorption capacities for 2-naphthol than for berberine hydrochloride and Congo red, and the modeling maximum adsorption capacities of 2-naphthol are in the range of 170.1-2680 mg/g. The adsorption equilibrium could be accomplished in 10, 40 and 30 min for 2-naphthol, berberine hydrochloride and Congo red, respectively. These results suggest metal chloride-assisted hydrothermal carbonization a promising method for converting biomass waste into effective adsorbents for wastewater treatment.

Comparative transcriptome analysis of Trichoderma reesei reveals different gene regulatory networks induced by synthetic mixtures of glucose and β-disaccharide

The mixture of glucose and β-disaccharide (MGD) synthesized by transglycosylation of glucose as a low-cost soluble carbon source can efficiently induce cellulase production in Trichoderma reesei, which holds potential for the biorefining of lignocellulosic biomass. However, it is not yet fully understood how MGD induces T. reesei cellulase. In this study, transcriptomic analyses were conducted to investigate the molecular basis of MGD for lignocellulose-degrading enzyme production of T. reesei Rut C30 compared with that on lactose. Particular attention was paid to CAZymes, transcription factors, transporters and other protein processing pathways related to lignocellulose degradation. As a result, MGD can elicit transcription of GH5-, GH6- and GH7-encoding cellulases that is up to 1.4-fold higher than that induced by lactose, but GH11- and GH74-encoding xylanases are downregulated by 1.7- and 4.4-fold, respectively. Gene expression profiles suggest that the transcription activators xyr1 and vib1 are significantly upregulated and that the mitogen-activated protein kinase pathway is strengthened compared to the case of lactose induction. In addition, hac1-encoding UPR-specific transcription factors are significantly upregulated by MGD, which may be enhanced due to proper folding and processing of nascent proteins. These findings provide a theoretical basis for further understanding the characterization of efficient cellulase production using MGD as an inducer in T. reesei and offer potential strategies for strain improvement.