Due to the limitations of traditional adsorbents for dyeing wastewater, this study combined natural adsorbent (CS, chitosan) and hydroxyapatite (HAp) to form a composite for enhancing the adsorption of aqueous Congo red (CR). The chitosan was prepared from crab shells (Somanniathelphusa sinensis) with a deacetylation degree of about 89%. The HAp and HAp-CS composites were prepared by precipitation in high pH (~10) with the help of concentrated ammonia water (25%). The crab shell chitosan and chitin were characterized by the FTIR method, and the HAp and HAp-CS composites were analyzed using the SEM method. The CR adsorption experiments were carried out in batch form and sampled once for each condition. The results showed that the characteristic peaks in the FTIR spectrum confirmed the success of the crab shell chitosan preparation. The HAp and HAp-CS composites possess porous structures and seem to have a high surface area. The CR adsorptions reached optimal after 5-15 min. contacting, the adsorption efficiency tended to decrease with the initial concentration of CR and increase with the adsorbent dosage. The initial pH of the solution affected the adsorption efficiency for the 70%HAp-CS and 30%HAp-CS composites but had almost no effect on the adsorption capacity of 0%HAp-CS and 50%HAp-CS. The 50%HAp-CS composite had the best adsorption capacity among the synthesized composites (qmax = 769.2mg/g). The adsorption isotherm and kinetics best fit the Langmuir isotherm and pseudo-second-order kinetics model.

Improving and exploring the photocatalytic performance of composites for new models continues to pose a challenge. Here, a straightforward thermal dispersion method is achieved by incorporating nitrogen (N) into TiO2 at different weights (1%, 3%, and 5%) to enhance photocatalytic activity. The material properties are analyzed through ultraviolet-visible diffuse reflectance spectroscopy (UV-VIS DRS), and X-ray diffraction (XRD). The results indicate that the NO gas removal efficiency of N-TiO2 photocatalytic materials is higher than that of pure TiO2 after 30 minutes of exposure to visible light. The highest NO gas treatment efficiency of N-TiO2 -1% is 40.4%, with a reaction rate following a first-order kinetic equation of 0.0688 min-1. Successfully fabricating N-TiO2 photocatalytic materials using the thermal dispersion method, with significantly enhanced photocatalytic performance under visible light activation, will benefit practical applications, particularly in the environmental sector.

Advanced materials have been of interest in recent years because of their outstanding properties that bring many useful applications to humans, they can be highly compatible with alternative materials. In particular, coating materials on HAp base increase the biocompatibility of HAp. In this study, we synthesize TiO2/HAp composite materials using the sol - gel method. Samples were made under different synthesis conditions in terms of HAp/TTIP ratios: (1:1); (1:1.5); (1:2); (1:2.5); (1:3). Factors affecting the synthesis process, such as the incubation time and pH of the solution, were also investigated. The optimal conditions for the synthesis process are the ratio HAp/TTIP: 1 gram HAp with 2 ml TTIP; stirring time: 16 hours; pH of the gel solution: pH = 0.5, as determined from the analysis of the X-ray diffraction spectrum and SEM surface morphology. The research results are the basis for research on biomedical materials.

Diatomite from Tuy An district, Phu Yen province, with different purities and diatom integrity as catalyst carriers, were adopted to prepare TNTs/g-C3N4 composite catalysts by a sol-gel method, with an optimal weight ratio of 1:1 for TNTs/g-C3N4 and diatomite. Compared with pure TNTs, g-C3N4, and TNTs/g-C3N4, the obtained composite photocatalysts exhibited lower photocatalytic performance under the same conditions and NO removal within 30 min under visible light. The NO gas treatment efficiency under the same conditions with different catalyst supports only decreases by approximately 18% at a reaction rate of 0.0950 min-1. This research on composite photocatalysts is a promising step towards practical environmental remediation. The use of diatomite as a carrier for photocatalytic materials is particularly noteworthy, as it is a naturally available and cost-effective source of materials. However, further improvements in the photocatalytic performance of the composite material are necessary to fully realize its potential in environmental remediation, including removing NOx and other pollutants. Overall, this study provides valuable insights into the influence of carriers on the photocatalytic activity of composite photocatalysts and lays the foundation for future research in this field.

S-TiO2 typically exhibits high photocatalytic activity, but its powdered form makes it difficult to apply practically in environmental treatment. Diatomite from different locations varies in purity and integrity of the diatomaceous earth, making it a suitable catalyst support for synthesizing mixed-phase S-TiO2 catalysts using the sol-gel technique. The synthesized photocatalyst exhibits similar photocatalytic activity to S-TiO2. The NO gas treatment efficiency under the same conditions with different catalyst supports only decreases by approximately 3% within 30 minutes at a reaction rate of 0.0950 min-1, with an optimal mass ratio of 70:30 for S-TiO2 and diatomite. This composite material holds promise for addressing the application of photocatalytic materials in practical environmental treatment, including NO removal and the treatment of other environmental pollutants, as diatomite is a naturally available and environmentally friendly material.