This review critically examines the latest advancements in clay mineral-based photocatalysts for water purification. Clay minerals, owing to their natural abundance, low cost, and unique physicochemical properties, have emerged as promising candidates for enhancing photocatalytic efficiency. This article delves into various activation methods for clay minerals, including acid, alkali, calcination, and mechanochemical activation, highlighting their roles in enhancing surface area, creating active sites, and improving photocatalytic performance. Moreover, the review explores various modification strategies for photocatalysts, such as doping with metal and non-metal ions, deposition of metals, and the design of heterojunctions, to further boost photocatalytic activity. In particular, the utilization of kaolinite, montmorillonite, attapulgite, and sepiolite as clay mineral supports for photocatalysts is discussed in detail, showcasing their potential in wastewater treatment. The review underscores the significant strides made in the development of clay mineral-based photocatalysts, highlighting their effectiveness in degrading organic contaminants under light exposure. Nevertheless, there are persisting challenges such as the optimization of loading quantities, improvement in compatibility between clay minerals and photocatalysts, and reduction in preparation costs for large-scale applications. In summary, this review offers valuable insights into the current status of clay mineral-based photocatalysts for water purification, thereby stimulating future research in this promising field.

The separation of magnesite from dolomite was studied by flotation tests, X-ray photoelectron spectroscopy (XPS), and zeta potential measurements in the presence of calcium ion (Ca²⁺) dissolved from dolomite. Sodium oleate (NaOL) was used as collector, and sodium carbonate (Na₂CO₃) and sodium hexametaphosphate (SH) were used as regulators. The results showed that SH had a good selective inhibition ability in pure mineral flotations of magnesite and dolomite. While in the presence of Ca²⁺ dissolved from dolomite, magnesite and dolomite were both inhibited by SH. The separation of magnesite from dolomite cannot be realized because Ca²⁺ can adsorb on the surface of magnesite in the form of CaCO₃ and change the surface properties of magnesite. Thus, the magnesite flotation was depressed. When the sequence of reagent addition was changed to add SH prior to Na₂CO₃, a complex was made by Ca²⁺ reacting with SH, which avoided the adsorption of Ca²⁺ on the magnesite surface and prevented the changing of the magnesite’s surface properties. Then, after adjusting the solution pH with Na₂CO₃, the flotation separation of magnesite from dolomite could be achieved.

The synergistic effect among flotation agents is why combined flotation agents exhibit superior performance compared to single flotation agents. This research investigates the influence of three surfactants with different charges of polar groups, sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), and octanol, combined with dodecylamine (DDA), on quartz flotation. Through the implementation of flotation tests, bubble–particle adhesion induction time testing, gas–liquid two-phase foam properties testing, and surface tension testing, it is revealed that substituting part of the DDA with these surfactants can either enhance or at least maintain the quartz recovery, affect the adhesion induction time, reduce the surface tension of the flotation system, and change the foaming performance and foam stability, depending on their mole ratio in the combined collector. Compared to DDA alone, combining CTAB or OCT with DDA can significantly increase quartz recovery, while SDS with DDA only yields an approximate recovery. Combining SDS or OCT with DDA can reduce the foam stability, while CTAB with DDA enhances the foam stability. The effect of the combination of surfactants and DDA on the adhesion induction time of quartz grains of different sizes with bubbles is the same; furthermore, there is a negative correlation between the adhesion induction time and the recovery, while the foaming properties and stability of foam are positively correlated with the recovery.

Hemimorphite and smithsonite are all-important zinc oxide minerals. The beneficiation and separation of them using flotation method is usually considered difficultly. Minerals surface wettability and its regulation are the core issues in the flotation process, which closely correlate with the surface properties of the minerals. Therefore, an in-depth understanding of the surface properties of the two minerals is of great significance for the study of the flotation technology of them. In this study, the surface properties of the hemimorphite (110) surface and the simthsointe (101) surface, and their relationships to the mineral floatability have been investigated by first-principle calculation method based on density functional theory. The calculation results demonstrated that the hemimorphite (110) surface exhibited more obviously surface reconstruction. For the orbital energy level of the surface atoms of two minerals, the O 2p orbital is closer to the Fermi level than the Zn 3d. Chemical bond Mulliken population value indicated that the ionicity of the unsaturated linkage on the smithsonite (101) surface was stronger than that on the hemimorphite (110) surface. The absolute values of the ratios of negative charges to positive charges on the surfaces of hemimorphite and smithsonite were 1.529 and 1.256 respectively. These results implied that the O atoms on hemimorphite (110) surface are more impede collector molecule, such as hydroximic acid, bond with Zn atom, hemimorphite (110) surface is more readily wetted by water. This study provides comprehension at an atomic level to the relationship between surface properties and the floatability of hemimorphite and smithsonite.

Research on the efficient flotation desilication of low-grade magnesite is of great significance for the sustainable development of magnesium resources. Traditional collectors usually have some disadvantages, such as poor selectivity, severe environmental pollution, and weak water solubility. To strengthen the desilication flotation process of magnesite ore, the biodegradable surfactant, cocamidopropyl amine oxide (CPAO), was first utilized as the collector for the separation of the magnesite and quartz. The selective adsorption behavior and mechanism of the quartz and magnesite with the CPAO as the collector were studied through the micro-flotation experiments of the single mineral and the artificially mixed mineral, contact angle and atomic force microscopy (AFM) measurements, fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analyses. The flotation results indicated that the CPAO showed good selectivity and could effectively separate magnesite and quartz. When the concentration of the CPAO was 10.0 mg/L in the natural pulp pH (about 7.2), the concentrates with 97.67% MgO recovery and 45.62% MgO grade were obtained. The contact angle and AFM measurements indicated that the CPAO could selectively adsorb on the quartz surface rather than the magnesite surface to improve the interface difference between them, especially its surface hydrophobicity. The results of the FTIR and XPS analyses indicated that the CPAO is selectively adsorbed on the surface of the quartz, mainly through electrostatic interaction and hydrogen bonding. In conclusion, the CPAO had good selectivity and great potential as an effective collector in the reverse flotation desilication progress of magnesite.

We demonstrate the microstructure and room-temperature H₂ sensing properties of undoped, Pt-doped, and Pd-doped SnO₂ nanowires (SNWs). SNWs with a tetragonal structure were synthesized by thermal evaporation of tin grains at 900 °C. Gas sensors based on undoped, Pt-doped, and Pd-doped SNWs showed a reversible response to H₂ at room temperature. The response was improved in the order undoped < Pt-doped < Pd-doped SNWs under the same conditions.