Waste straw contains a large amount of lignin, and its resource utilization is not only in line with the national double carbon development strategy, but also to alleviate environmental pollution. Hydrothermal carbonization is a new thermochemical conversion technology, which has attracted much attention because it can directly transform carbon containing waste raw materials with high moisture content and low energy density. To investigate the physicochemical properties and aromatization changes of lignin hydrochar, hydrothermal carbonization experiments were carried out at 290 °C and a solid–liquid ratio of 1:20 for 0.00, 0.25, 0.50, 1.00, 1.50, 2.00, 4.00, 8.00 h, respectively. The experimental results shows that hydrothermal carbonization can increase the combustion quality of lignin. Physical and chemical properties analysis shows that with the increase of hydrothermal carbonization time from 0 to 2 h, the hydrochar content increased from 21.21% to 26.02% and the HHV of hydrochar increased from 20.01 MJ/Kg to 26.32 MJ/Kg. When the holding time exceeded 2 h, the carbon content and calorific value of hydrothermal tended to be stable. With the increase of holding time, FTIR analysis and XRD analysis show that the free hydroxyl groups in water-soluble lignin were easily combined with intramolecular and intermolecular hydrogen bonds, thus forming an ordered crystal arrangement. Subsequently, the crystal structure formed a well-arranged long chain through a strong hydrogen bond network, forming a ring structure in the process of aromatization. Aromatic ring structure accumulated, aromatization wave peak increased with holding time and aromatization intensified. Hydrochar crystal particles became larger and arranged in order. At the same time, the surface functional group detection and degree of crystallization were almost unchanged when holding time exceeded 2 h. The surface morphology of hydrochar was observed by SEM as follows: when the hydrothermal carbonization reaction of lignin entered the insulation stage, the microsphere structure began to aggregate and then became larger. When the holding time reached 2 h, the growth rate of carbon microspheres noticeably slowed. Therefore, the optimal hydrothermal carbonization time of lignin is 2 h, and hydrochar fuel has the best performance and aromatization.

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.

To enhance the hydrothermal carbonization (HTC) process on biomass waste and improve the quality of biomass solid fuel. Corn straw was pretreated with acid washing and subsequently hydrothermally carbonized at 180–270 °C. The solid product obtained (hydrochars) was compared with the solid product produced from untreated hydrothermally carbonized straw. The results show that the acid pretreatment removed 7.9% of the ash from the straw. ICP and XRD analysis show that most of the alkali and alkaline earth metals have been removed. This addresses the defect of high ash content as the HTC temperature increases. The HHV of hydrochars produced by HTC after acid washing can reach 27.7 MJ/kg, which is nearly 10% higher than that of hydrochars prepared without acid washing pretreatment, and nearly 70% higher than that of straw raw materials. Elemental analysis and FTIR analysis show that the acid washing pretreatment changed the content and structure of the biomass components in the straw, resulting in a more complete HTC reaction and higher carbon sequestration. The decrease of H/C and O/C deepened the degree of coal-like transformation of hydrochars, with the lowest approaching the bituminous coal zone. The combustion characteristics of the hydrochars prepared after acid washing were significantly upgraded, the comprehensive combustion index and thermal stability of hydrochars both increased. Therefore, HTC after acid washing pretreatment is beneficial to further improve the high heating value and combustion characteristics of hydrochar.

In order to reduce building energy consumption and make wall insulation materials meet fire protection requirements, the authors put forward a kind of energy saving model of building exterior wall under green and energy saving nanomaterials. Mainly using PBECA energy saving calculation software. By setting up multi-component, multi-material method. The energy consumption of building aggregate in light energy saving device modified by nanomaterials is simulated and analyzed, and the energy consumption of building agent area is compared. The energy saving effect of light energy saving system modified by nanomaterial fly ash in prefabricated buildings was verified. According to the calculation of PBECA energy-saving calculation software, the annual energy consumption of the building assembled by nanomaterials modified fly ash lightweight energy-saving units is 5981 kWh, and the energy consumption per unit area is 35.01 kWh/m2. In the 1980's, the annual energy consumption of household agents was 86237 kWh, and the energy consumption per unit area was 50.42 kWh/m2. Through the analysis of the calculation results, it is concluded that the energy saving efficiency of replacing the light-saving wall with nanomaterials fly ash in precast area A can reach 65% of the energy saving standard.

Hydrothermal carbonization (HTC) and Fenton pretreatment (FP) are effective methods currently being used to treat lignin. However, there are few reports of combining the two techniques and applying them in the treatment of lignin. Additionally, the synergistic effect of the two techniques on the physicochemical properties of lignin has not been widely investigated. Therefore, this study innovatively combined Fenton pretreatment with hydrothermal carbonization to investigate the synergistic effect on two types of structurally different lignans, and to reveal the changes in physicochemical properties of lignin under the synergistic effect. In this work, ¹³C NMR, XPS, FTIR, XRD, Raman spectroscopy, and automated calorimetry were used to determine the physicochemical properties and characterize the chemical structure of lignin. The results showed that the synergistic effect of FP–HTC increased the carbon fixation rate of herbal lignin (HL) and de-alkalized lignin (DAL) by 46.07 and 59.27%, respectively, and heating value of HL and DAL by 45.53 and 46.07%, respectively. The synergistic action of FP–HTC broke the stubborn and complex chemical barrier of lignin, and effectively enhanced the degree of aromatization and demethoxylation of lignin. It is notable that the synergistic effect of FP–HTC induced the formation of more stable 4-O-5 bonds and C–C bonds in the lignin structure, resulting in a moderate enhancement of the lignin chemical structure and material properties. In this study, the synergistic effect of Fenton pretreatment and hydrothermal carbonization is utilized to convert lignin into sustainable carbon materials, and the effect of the synergistic effect on the physicochemical properties of lignin is analyzed in detail, which provides valuable references for the subsequent research on the conversion of waste lignin into carbon materials.