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Abstract This research examines the efficacy of layered double hydroxides (LDHs) in removing phosphate and nitrate from wastewater, enhanced by the memory effect and in situsynthesis techniques. LDHs were synthesized hydrothermally, initially creating carbonate-based CO₃–LDHs, which were then converted to chloride-based Cl–LDHs through anion exchange. These LDHs underwent calcination at 300 °C, 400 °C, and 500 °C to optimize their structure for enhanced adsorption capabilities. The synthesized LDHs were thoroughly characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET) surface area analysis, and X-ray diffraction (XRD). Adsorption experiments in solutions with pH values between 5, 7, and 9 revealed the adsorption capacities of phosphate and nitrate on the CO₃–LDHs and Cl–LDH, respectively. The results indicated that LDHs calcined at 500 °C showed the highest adsorption performance, achieving maximum capacities of 184 mg/g for phosphate and 70.1 mg/g for nitrate. Kinetic studies confirmed that the adsorption process followed a pseudo-second-order model, demonstrating the effectiveness of the memory effect in enhancing ion exchange. The in situ synthesis of LDHs under controlled conditions significantly improved the removal rates of these anionic contaminants from wastewater, proving the potential of this method for the realistic wastewater treatment.

Abstract Ettringite is a hydrous calcium aluminum sulfate mineral present in cement. In this study, ettringite was synthesized via co-precipitation to remove methyl blue, dichromate, and copper ions from solutions with various pH values. The synthesized ettringite was characterized using scanning electron microscopy, X-ray photoelectron spectrometry, Fourier transform infrared spectroscopy, zeta potential analysis, and the Brunauer–Emmett–Teller method. Equilibrium adsorption experiments were performed using methyl blue and dichromate at pH values ranging from 5 to 11. To avoid precipitation, equilibrium adsorption experiments were performed on copper ions in solutions with pH values of 3, 4, and 5. The adsorption kinetics experiments for each contaminant were performed at pH 5. The results showed that ettringite was successfully synthesized, and calcite might have precipitated during the synthesis process. The point of zero charge was at pH 8.6. The maximum adsorption capacities for methyl blue, dichromate, and copper ions at pH 5 were 406, 321, and 365 mg/g, respectively. The adsorption kinetics fitted the pseudo-second-order model well. The properties of the contaminants affect their equilibrium and rate constants. Ion exchange is regarded as the primary adsorption mechanism, whereas the other mechanisms include complexation, hydrogen bonding, surface precipitation, π-interaction, and van der Waals forces. This study revealed a new adsorbent, ettringite, for the removal of contaminants from wastewater, which is a promising alternative adsorbent that can be used under specific conditions.

One of the concerns for applying STEM education in the classroom is students’ participation. In this study, the Engagement and Participation in Classroom – Science (EPIC-S) questionnaire was applied to explore Vietnamese students’ participation behaviors and their perceptions of the science classroom environment. The main goal of our study was to investigate the impact of students’ classroom participation on their perceptions of the science classroom environment as assessed by the EPIC-S questionnaire. Our survey was conducted on 884 students in some public secondary schools in Vietnam and the collected data was analyzed using SPSS 20. Students were classified into two groups-verbal and silent- based on how they participated in several facets of the science classroom environment. We found no statistically significant difference between these two groups in their perception of the relationship with the teacher. Nevertheless, there are differences in their perceptions of peer support, fear of embarrassment, and teacher openness. Our results will contribute to the theoretical background for STEM education in Vietnam

Titanium dioxide/graphene aerogel (TiO2/GA) was synthesized via a one-pot hydrothermal method and characterized by various spectroscopic techniques, including X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscopy, Raman spectroscopy, and UV-Vis spectroscopy. The influences of pH and TiO2/GA dose on the photocatalytic performance were investigated against positive dye methylene blue (MB) under UV light control. The characterization of TiO2/GA revealed that the synthesized TiO2 nanosize of 12–22.5 nm was uniformly distributed onto the graphene layers. The bandgap of the as-prepared nanocomposite was 2.63 eV, lower than that of pure TiO2 (3.2 eV). The kinetic studies exhibited that the adsorption–desorption equilibrium was achieved after 60 min following the pseudo-second-order. Meanwhile, 99.9% of MB was eliminated after 120 min at pH 9 with a 20 mg catalyst. The degradation data were well fitted to the pseudo-first-order kinetic model. Accordingly, applying TiO2/GA as an efficient photocatalyst indicates a potential pathway for the degradation of organic contaminants in wastewater treatment.

Manganese (Mn) serves as an essential micronutrient within the intricate nexus of soil-plant-microbial interactions, playing a pivotal role on various physiological processes crucial for optimal plant growth. Tan Cuong commune of Thai Nguyen province stands out as a distinctive tea production region in Vietnam, characterized by prolonged tea cultivation accompanied by intensive applications of chemical fertilizers, thereby exerting notable and discernible effects on the physicochemical properties of the soil. The objectives of this study were to investigate the distribution and fractionation of Mn in tea soils, with a specific focus on the prevailing context of soil acidification. The study involved a comprehensive analysis of six distinct Mn fractions within soil profiles under tea gardens and adjacent forested patches. The findings revealed a marked accumulation of specific Mn fractions in surface horizons, exhibiting a declining trend with increasing soil depth across the majority of the study sites. Notably, both tea and forest soils, the Entisols, in flat river plain area presented a special distribution of Mn fractions throughout the soil depth. The observed soil acidification resulting from tea cultivating practices was associated with an augmented solubility of Mn fractions that were previously inaccessible, facilitating plant absorption and contributing to leaching losses. The multifaceted interactions elucidated in this research furnish valuable insights for informed agricultural practices, thereby safeguarding the quality and productivity of tea plants amidst evolving environmental conditions. [ABSTRACT FROM AUTHOR]