High yield self-nitrogen-oxygen doped hydrochar derived from microalgae carbonization in bio-oil: Properties and potential applications

Deep learning prediction and experimental investigation of specific capacitance of nitrogen-doped porous biochar

N-doped porous biochar is a promising carbon material for supercapacitor electrodes due to its developed pore structure and high chemical activity which greatly affect the capacitive performance. Predicting the capacitance and exploring the most influential factors are of great significance because it can not only avoid the trial-and-error experiments but also provide guidance for the synthesis of biochar with the aim of capacitance enhancement. In this study, a CNN model with ReLU activation function was established using DenseNet architecture for specific capacitance prediction. The importance and impacts of the physiochemical properties of N-doped porous biochar to the capacitance were revealed. With the guidance of the model, N-doped porous biochar samples with high capacitance were synthesized, the data of which were further used for model validation. This study provides not only a deep learning model which can be used in practice for capacitance prediction but also directions for the synthesis of N-doped porous biochar with high capacitive performance.

Fe/N co-doped magnetic porous hydrochar for chromium(VI) removal in water: Adsorption performance and mechanism investigation

Four kinds of Fe/N co-doped porous hydrochar were prepared by one/two-step N-doping schemes using microwave/traditional pyrolysis methods for removing Cr(VI) from aqueous phase. Heterocyclic-N was introduced through CO(NH2)2-based hydrothermal carbonization process, which could adjust the electronic structure of the hydrochar framework. Furthermore, Fe0 and Fe3O4 were embedded into hydrochar via carbothermal reduction reaction using FeCl3 as the precursor, which improved the reducibility and magnetism of the material. The modified hydrochar exhibited pH-dependency and rapid kinetic equilibrium, and the maximal adsorption amount of magnetic porous hydrochar obtained by microwave-assisted one-step N-doping (MP1HCMW) reached 274.34 mg/g. Meanwhile, the modified hydrochar had a high tolerance to multiple co-existing ions and the removal efficiency maintained above 73.91 % during five regeneration cycles. Additionally, MP1HCMW efficiently removed Cr(VI) via pore filling, electrostatic attraction, ion exchange, reduction, complexation, and precipitation. Summarily, Fe/N co-doped porous hydrochar was a feasible adsorbent with outstanding remediation potential for Cr(VI)-contaminated water.

Research progress on pyrolysis of nitrogen-containing biomass for fuels, materials, and chemicals production

Pyrolysis of nitrogen-containing biomass holds tremendous potential for producing varieties of high value-added products, alleviating energy depletion. Based on the research status about nitrogen-containing biomass pyrolysis, the effect of biomass feedstock composition on pyrolysis products is first introduced from the aspects of elemental analysis, proximate analysis, and biochemical composition. The properties of biomass with high and low nitrogen used in pyrolysis are briefly summarized. Then, with the pyrolysis of nitrogen-containing biomass as the core, biofuel characteristics, nitrogen migration during pyrolysis, the application prospects, unique advantages of nitrogen-doped carbon materials for catalysis, adsorption and energy storage are introduced, as well as their feasibility in producing nitrogen-containing chemicals (acetonitrile and nitrogen heterocyclic) are reviewed. The future outlook for the application of the pyrolysis of nitrogen-containing biomass, specifically, how to realize the denitrification and upgrading of bio-oil, performance improvement of nitrogen-doped carbon materials, as well as separation and purification of nitrogen-containing chemicals, are addressed.

Critical Review on Nanomaterials for Enhancing Bioconversion and Bioremediation of Agricultural Wastes and Wastewater

Anaerobic digestion (AD), microalgae cultivation, and microbial fuel cells (MFCs) are the major biological processes to convert organic solid wastes and wastewater in the agricultural industry into biofuels, biopower, various biochemical and fertilizer products, and meanwhile, recycle water. Various nanomaterials including nano zero valent irons (nZVIs), metal oxide nanoparticles (NPs), carbon-based and multicompound nanomaterials have been studied to improve the economics and environmental sustainability of those biological processes by increasing their conversion efficiency and the quality of products, and minimizing the negative impacts of hazardous materials in the wastes. This review article presented the structures, functionalities and applications of various nanomaterials that have been studied to improve the performance of AD, microalgae cultivation, and MFCs for recycling and valorizing agricultural solid wastes and wastewater. The review also discussed the methods that have been studied to improve the performance of those nanomaterials for their applications in those biological processes.

N,N-Dimethylformamide solvent assisted hydrothermal pretreatment of Chlorella for coproduction of sugar, nitrogenous compounds and carbon dots

Microalgae are considered as a promising alternative to fossil fuels due to their ease of cultivation, short growth cycle and no occupation of cultivated land. In this study, N,N-Dimethylformamide (DMF) solvent was employed to assist hydrothermal pretreatment of Chlorella for coproduction of sugar, nitrogenous compounds and carbon dots (CDs). The effect of pretreatment conditions on the composition and pyrolysis bio-oil distribution of hydrothermal solid residues as well as CDs characteristic were investigated by varying the temperature (180-220 ℃) and reaction time (1-9 h). The results showed that pretreated residues had higher cellulose. And the yield of sugar and N-contained compounds reached 41.59% and 63.57% in the pyrolysis bio-oil of pretreated algae residues, respectively. Moreover, CDs obtained from hydrothermal solution fluoresced red under 365 nm excitation. The paper provides a new method for the complete utilization of microalgae.

Synergistic effects of lanthanum ferrite perovskite and hydrogen to promote ammonia production during microalgae catalytic pyrolysis process

Ammonia (NH₃) production from nitrogen-enriched renewable resources pyrolysis is a green, clean, and sustainable technology. In this paper, lanthanum ferrite perovskite (LaFeO₃) and hydrogen (H₂) atmosphere were combined to enhance NH₃ production during microalgae pyrolysis. The catalytic pyrolysis of microalgae pyrolysis was carried out in a fixed bed reactor. The results show that the synergistic effects between H₂ and LaFeO₃ promote the fuel-nitrogen transfer into gas phase, while nitrogen in biochar and bio-oil significantly decreases. H₂ and LaFeO₃ not only favor the conversion of protein-N to pyridinic-N, pyrrolic-N, and quaternary-N in char, but also accelerate the deamination of amides, pyrroles, and pyridines, thus facilitating the formation of NH₃. Pyrolysis temperature plays a considerable role in distribution and conversion of N-species. Increasing temperature increases NH₃ and HCN yields, the maximum NH₃ yield reaches 47.40 wt% at 800 °C. Moreover, LaFeO₃ shows considerable stability during 10 cyclic operations.

Potential of yak dung-derived hydrochar as fertilizer: Mechanism and model of controlled release of nitrogen

Improving fertilizer efficiency with assistance of biochar has drawn much attention in sustainable agriculture. Promoting slow-release properties of biochar itself with cost-effective production technology is a pressing demand. In this study, hydrochar derived from nutrition-enriched yak dung (HC) and corresponding controlled release nitrogen fertilizer (HCRNF) via HCl modifying were studied, and the slow release performance as well as mechanisms were investigated. The results show that HCRNF presents a better N controlled-release performance with cumulative N release amounts of 56.01%-70.30% compared with 72.60%-78.45% of HC. The specific surface area reached highest 47.161 m²·g^-1 in HCRNFs with the pore volume of 0.098 cm³·g^-1. Hydrochloric acid modification treatment increases the surface acid group contents such as phenolic hydroxyl group content increasing to 1.48 mmol·g^-1 in HCRNF250. Because the porous structure and stable internal force between N and O-containing functional groups are improved, the N desorption from HCRNF is retarded, which shows a controlled release behavior. We concluded that the HCRNF via HCl modification in this work has a great application potential as slow released N fertilizer in sustainable green agriculture.