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.