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.

Hydrothermal carbonization (HTC) is an efficient method for converting lignocellulosic biomass into biofuels. However, traditional Brønsted acid-catalyzed HTC processes face challenges such as high costs and limited catalytic efficiency. In this study, the catalytic carbonization mechanism was investigated within the temperature range of 180–220 °C by analyzing the evolution of functional groups in hydrochar under lanthanide (III)-catalyzed and non-catalyzed conditions. The results indicate that compared to acid catalysis, lanthanide (III) exhibits superior catalytic performance during the low-temperature HTC of cellulose. At 200 °C, lanthanide (III) accelerates the conversion of cellulose into char microparticles, while at 220 °C, it promotes the complete hydrolysis of cellulose into char microparticles enriched with furan structures. Characterization analyses revealed that lanthanide (III) enhances the formation of HMF (5-hydroxymethylfurfural), suppresses its conversion to LA (levulinic acid), promotes the polymerization of HMF into char microparticles, and indirectly accelerates the hydrolysis of cellulose into oligosaccharides.

The characteristics of water-soluble ions in indoor PM_2.5 during the Spring Festival in Changchun City were analyzed by ion chromatography. The results showed that the main water-soluble ionic components in the indoor and non-combustion periods were SO₄ ²- and Ca²⁺, and the concentration of Na⁺, K⁺, Mg²⁺, F^-, Cl^- and NO₃ ^- increased in the fireworks and firecrackers, among which Cl^- and NO₃ ^-. The concentration increased significantly compared with the non-combustion period, and peaked with PM_2.5 concentration in the first month of the first month and the first month of the first month; the correlation between NH₄ ⁺ and SO₄ ²- during the discharge and non-combustion periods was greater than the correlation between NH₄ ⁺ and NO₃ ^-, NH₄ ⁺ Sulfate is preferentially combined with SO₄ ²-, and secondary ions are mainly in the form of (NH₄)₂SO₄ and NH₄NO₃. Cluster analysis and correlation analysis indicate that the sources of water-soluble ions in indoor PM_2.5 during the Spring Festival can be classified into four categories. Biomass combustion source, automobile exhaust gas source, coal-fired emission source and soil dust, among which the main sources of Na⁺, K⁺, Mg²⁺, Cl^-, SO₄ ²- during the discharge period are the fireworks and firecrackers.

To monitor the soil temperature field of a ground source heat pump project in Changchun and research their variation and influencing factors. Research showed that: the soil temperature field with the heat pump heating/cooling alternate operation present a periodic variation. The impact of outdoor temperature on the soil temperature field gradually weakened with the increase of the depth and after-10m the change tend to be the same. In transition season soil self-recovery capability is very limited, ground source heat pump system under the condition of cold and hot load imbalance to run for a long time inevitable emergence of thermal imbalance phenomenon.