Shuguang Yang’s research while affiliated with State Key Laboratory of Mineral Deposit Geochemistry and other places

The interaction between aluminum (hydr)oxides and inorganic substances has received widespread attention in the fields of ore deposit geochemistry, mineral processing, and environmental protection [...]

This research delved into the influence of mesoporous silica’s surface charge density on the adsorption of Cu²⁺. The synthesis of mesoporous silica employed the hydrothermal method, with pore size controlled by varying the length of trimethylammonium bromide (CnTAB, n = 12, 14, 16) chains. Gas adsorption techniques and transmission electron microscopy characterized the mesoporous silica structure. Surface charge densities of the mesoporous silica were determined through potentiometric titration, while surface hydroxyl densities were assessed using the thermogravimetric method. Subsequently, batch adsorption experiments were conducted to study the adsorption of Cu²⁺ in mesoporous silica, and the process was comprehensively analyzed using Atomic absorption spectrometry (AAS), Fourier transform infrared (FTIR), and L3 edge X-ray absorption near edge structure (XANES). The research findings suggest a positive correlation between the pore size of mesoporous silica, its surface charge density, and the adsorption capacity for Cu²⁺. More specifically, as the pore size increases within the 3–4.1 nm range, the surface charge density and the adsorption capacity for Cu²⁺ also increase. Our findings provide valuable insights into the relationship between the physicochemical properties of mesoporous silica and the adsorption behavior of Cu²⁺, offering potential applications in areas such as environmental remediation and catalysis.

The direct discharge of rare earth wastewater causes the waste of resources and heavy metal pollution. This paper compared the adsorption behaviors of lanthanide ions on bentonite under sulfate and nitrate systems by examining the factors affecting the adsorption, such as adsorption time, pH, background electrolyte concentration, and initial rare earth ion concentration. It was shown that the sulfate system was more favorable for the adsorption of rare earth ions on the bentonite surface. The maximum adsorption capacity in the sulfate system was about 1.7 times that in the nitrate system. In contrast, the adsorption under the nitrate system was more sensitive to the changes in pH and background electrolyte concentration. The adsorption processes under both systems are spontaneous physical adsorption processes (ΔGθ are from −27.64 to −31.48 kJ/mol), and both are endothermic (ΔHθ are 10.38 kJ/mol for the nitrate and 7.53 kJ/mol for the sulfate) and entropy-increasing (ΔSθ are 61.54 J/mol for the nitrate and 76.24 J∙mol⁻¹ for the sulfate) processes. This study helps to provide information about the optimizing process parameters for the adsorption treatment of rare earth wastewater using bentonite.

This research delved into the influence of mesoporous silica's surface charge density on the adsorption of Cu ²⁺ . The synthesis of mesoporous silica employed the hydrothermal method, with pore size controlled by varying the length of trimethylammonium bromide (C n TAB, n = 12,14,16) chains. Gas adsorption techniques and transmission electron microscopy characterized the mesoporous silica structure. Surface charge densities of the mesoporous silica were determined through potentiometric titration, while surface hydroxyl densities were assessed using the thermogravimetric method. Subsequently, batch adsorption experiments were conducted to study the adsorption of Cu ²⁺ in mesoporous silica, and the process was comprehensively analyzed using Atomic absorption spectrometry (AAS), Fourier transform infrared (FTIR), and L3 edge X-ray absorption near edge structure (XANES). The research findings suggest a positive correlation between the pore size of mesoporous silica, its surface charge density, and the adsorption capacity for Cu ²⁺ . More specifically, as the pore size increases within the 3-4.1 nm range, the surface charge density and the adsorption capacity for Cu ²⁺ also increase. Our findings provide valuable insights into the relationship between the physicochemical properties of mesoporous silica and the adsorption behavior of Cu ²⁺ , offering potential applications in areas such as environmental remediation and catalysis.

Many surface processes of clay minerals require in-depth understanding of their surface electrical properties, such as surface charge density, surface potential distribution, etc. In this paper, electrostatic force microscopy (EFM) and Kelvin probe force microscopy (KPFM) were used to study the surface charge densities, surface potentials, electric field intensities, and electric field force gradients of three common clay minerals: kaolinite, montmorillonite, and illite. The properties were directly imaged, and the average surface permanent charge densities of kaolinite, montmorillonite, and illite were obtained to be -0.0060, -2.136, and -5.456 μC m ⁻² , respectively. In addition, a good linear relationship was found between the surface charge densities obtained by KPFM and the layer charges calculated from the mineral chemical formulas of three clay minerals.

The enrichment process of rare earth elements in ion-adsorbed rare earth ores and bauxite is potentially related to the adsorption of rare earth elements by gibbsite. In this paper, lanthanum and yttrium were selected as surrogates of light rare earth elements and heavy rare earth elements, respectively. The effects of adsorption time, solution pH, and background electrolyte concentration on the adsorption of rare earth ions by gibbsite were investigated through batch adsorption experiments. The results showed that the adsorption of rare earth ions by gibbsite can approach equilibrium in 72 h. There is mainly electrostatic repulsion between gibbsite and rare earth ions at pH 4–7, and the adsorption efficiency increases with the increase in solution pH value and background electrolyte concentration. The adsorption process of rare earth ions by gibbsite is more consistent with the pseudo-second-order kinetic and Langmuir single-layer adsorption models. Moreover, based on the structural correlation between clay minerals and gibbsite, the causes for the differences in the adsorption behaviors of rare earth elements on the minerals are discussed. The results of this study help to understand the role of aluminum hydroxide in the migration and fate of rare earth elements in epigenetic environments.

Heat treatment is routinely utilized in preparing nanoporous materials (including Stöber silica), and can substantially affect their performance in diverse application fields. However, the effects of heat treatment at different temperatures on the structure and surface properties of Stöber silica have not been systematically investigated before. In this work, Stöber silica (washed with water or ethanol) was calcined at different temperatures (from 250 °C to 1000 °C), and the heat-treated samples were characterized through nitrogen adsorption at 77 K, scanning electron microscopy, simultaneous thermal analysis, elemental analysis, and Fourier-transform infrared spectroscopy. The results show that there is no significant difference in the morphology and particle size of the calcined samples. The internal micropores almost collapse after calcination at 500 °C, and the pores with a smaller diameter are the first to shrink during calcination. The variation in the number of the surface hydroxyl groups and ethoxyl groups with the calcination temperature is discussed in detail. The carbon content analysis and differential scanning calorimetry curves reveal that the surface ethoxyl groups (for the samples washed with ethanol) are completely removed after calcination at 500 °C. After calcination at temperatures above 800 ℃, the hydroxyl groups almost completely condense into siloxanes. The specific surface area calculated according to the thermogravimetric mass loss and surface hydroxyl density is found to be significantly different from the measured Brunauer–Emmett–Teller specific surface area. Our results may offer practical guidance for the application of Stöber silica subjected to similar heat-treatment processes.

Organic matter (OM) in shales occurs as nanometer-sized intercalations with clay minerals that are termed as clay-organic nanocomposites; however, the OM occurrence in nanocomposites at different stages of maturation is still unclear, and the co-evolution process of OM and clay under burial is not well understood. To reveal the variation of OM occurrence and clarify the relationship between petroleum generation of OM & transformation of clay minerals in nanocomposites as a function of maturity, this study investigates the structure and clay-OM association in 44 samples from three leading shales at different maturity stages from two basins in China. A total of 15 samples of lacustrine shale from upper Triassic Yanchang Formation, 15 samples of marine shale from Lower Silurian Longmaxi Formation, and 14 samples of marine shale from Lower Cambrian Niutitang Formation were analyzed based on organic geochemistry, X-ray diffraction (XRD), and field emission-scan electron microscopy (FE-SEM), focused ion beam (FIB) sample preparation and consequent high resolution-transmission electron microscopy (HR-TEM) observations combined with energy dispersive spectroscopy (EDS). The results from this study show that most shale samples are organic-rich, and these three shales represent thermal evolutionary process from oil-window mature to overmature in a sequence of Triassic Yanchang, Silurian Longmaxi, and Cambrian Niutitang formations. Thorough observations indicate that sub-parallel bands of clays and intermingling of detrital minerals (such as quartz) dominate the nanocomposites in the Yanchang samples. While for Longmaxi and Niutitang shales, abundant nanopores and pyrite nanoparticles are observed in nanocomposites with features of layered distributions of OM and clay minerals. The structural investigation of nanocomposites shows that organic carbon between multi-layers dominates the OM occurrence in nanocomposites, which significantly extends the traditional opinion of OM-clay association. At an oil-window mature stage, the fluctuational interlayer spacing and a certain intensity of the carbon peak observed in the EDS spectra for corresponding clays provide a visual evidence of the organic molecules accessing the monolayer spaces of smectite. With the evolutional process of nanocomposites in shale and petroleum generation of OM & mineral transformation (illitization of smectite) running in parallel, it is inferred that the organic molecules migrate from monolayer spaces as gaseous hydrocarbons are generated, and eventually form stable clay-organic nanocomposites at an overmature stage. The results presented here will contribute to an improved understanding of diagenesis and organic-inorganic interactions in OM-rich shales.

Nanoplastics (NPs) are emerging contaminants in the environment, where the transport and fate of NPs would be greatly affected by interactions between NPs and minerals. In the present study, the interactions of two types of polystyrene nanoplastics (PSNPs), i.e., bare-PSNPs and carboxylated PSNPs-COOH, with iron (hydr)oxides (hematite, goethite, magnetite, and ferrihydrite), aluminum (hydr)oxides (boehmite and gibbsite), and clay minerals (kaolinite, montmorillonite, and illite) were investigated. The positively charged iron/aluminum (hydr)oxide minerals could form heteroaggregates with negatively charged PSNPs. Electrostatic and hydrophobic interaction dominate for the heteroaggregation of bare-PSNPs with iron/aluminum (hydr)oxide minerals, while ligand exchange and electrostatic interaction are involved in the heteroaggregation of PSNPs-COOH with iron/aluminum (hydr)oxides minerals. However, heteroaggregation between PSNPs and negatively charged clay minerals was negligible. Humic acid markedly suppressed such heteroaggregation between PSNPs and minerals due to enhanced electrostatic repulsion, steric hindrance, and competition of surface attachment sites. The heteroaggregation rates of both bare-PSNPs and PSNPs-COOH with hematite decreased with increasing solution pH. Increased ionic strength enhanced the heteroaggregation of PSNPs-COOH but inhibited that of bare-PSNPs. The results of the present study suggested that the heteroaggregation of PSNPs in environments could be strongly affected by minerals, solution pH, humic acid, and ionic strength.

The pyrolytic behavior of organic matter inside nanopores was studied by simultaneous thermogravimetric/differential scanning calorimetry analyzer coupled with Fourier transform infrared spectroscopy (STA/TG-FTIR). Nanoporous silica was prepared by a hydrothermal method using long-chain alkyl quaternary ammonium bromide (C n TAB, n = 12, 14) as a template. The pyrolytic behavior of C n TAB inside nanopores with different diameters was investigated and compared with that of C n TAB inside and outside nanopores. The results showed that the pyrolytic removal process consisted of the following features: 1) C n TAB underwent carbon chain decomposition and oxidation; 2) the DSC exothermal peak of C n TAB came mainly from its oxidative combustion, and the oxidative combustion temperature decreased with increasing pore size; 3) the C n TAB inside nanopores underwent crystallization–amorphous state phase transition, and C n TAB got trapped inside the calcined nanopores. In addition, the pyrolytic behavior of C n TAB inside the calcined nanopores was found to be similar to that of the uncalcined nanopores. This study aims to understand the storage and transformation processes of organic hydrocarbons under nanopore-confinement effect.