Construction of three-dimensional g-C3N4/attapulgite hybrids for Cd(II) adsorption and the reutilization of waste adsorbent

[Display omitted] •g-C3N4 was immobilized on ATP by a facile freeze drying-calcination method.•The defects N sites from g-C3N4 attributed to the enhanced Cd(II) adsorption.•The saturated g-C3N4/ATP was converted to CdS/g-C3N4/ATP for photocatalysis. Here we report a graphitic-C3N4 (g-C3N4) modified ATP adsorbent, g-C3N4/ATP, to enhance the adsorption of Cd(II) ion in wastewater, and the as-prepared adsorbent could be recovered as a CdS/g-C3N4/ATP photocatalyst utilized for the degradation of antibiotic pollutant. Due to the surface defects of g-C3N4 caused by the tri-s-triazine (C6N7) units, ATP could be bounded with g-C3N4 strongly. The combined adsorption sites, that the surface hydroxyl on ATP and the defected N sites on g-C3N4 attributed to the enhanced Cd(II) adsorption on g-C3N4/ATP hybrid (CA-0.50), which was 61.1 mg·g−1 and reached to the 1.76 times of that on the raw ATP. Meanwhile, due to the flexible structure of g-C3N4, the g-C3N4/ATP hybrid possessed a three-dimensional structure, and favored to improve the stability of adsorption by locking the adsorbed Cd(II). The Cd(II) adsorption on g-C3N4/ATP was well fitted the Langmuir isotherms model and exhibited the monolayer adsorption. For the recovered CdS/g-C3N4/ATP composite, it exhibited an excellent performance in the photodegradation of tetracycline with low concentration (25 ppm), on which the mineralization efficiency of tetracycline reached to 59.7% in 15 min under simulated solar light irradiation.