Highly efficient adsorption and visible-LEDs-driven photodegradation of tetracycline over novel and green-synthesized p-BiOI/n-Bi2WO6 heterojunctions

Abstract

Preparing bismuth compounds-based heterojunctions with superior redox capability has emerged as a promising strategy for environmental remediation. Herein, p-BiOI/n-Bi₂WO₆ heterojunctions were successfully obtained via a novel, facile, and green solvothermal method. The heterojunctions were synthesized using different mass ratios (1:2, 1:1, and 2:1) of BiOI (BI) and Bi₂WO₆ (BW), with 1:1 as the best ratio, which was decorated with silver nanoparticles (Ag-NPs) and nitrogen-doped graphene (NG) applying green methodologies. The as-prepared BI/BW heterojunctions were characterized by several techniques, and their adsorption capacity and photodegradation activity toward tetracycline (TC) under 19 W visible LEDs illumination were investigated. The capacity of pure BI, BW and BI/BW heterojunctions for adsorbing TC ranged from 14 to 68 mg/g; among the heterojunctions, Ag/1BI/1BW showed the highest TC adsorption capacity, 35 mg/g. Moreover, the photocatalytic tests revealed that the Ag/1BI/1BW exhibited the highest catalytic performance, achieving a TC percentage degradation of 81 % within 120 min. The low nominal power consumption of the LED-based photoreactor (0.0475 kWh) was significantly lower than that reported in the literature for using Xe or Hg lamps. In addition, catalyst dosage, initial TC concentration, and solution pH were investigated, demonstrating that they play important role in TC photodegradation. Scavenger assays determined that the degradation of TC using Ag/1BI/1BW proceeds mainly via superoxide radicals and holes, which agrees with the carrier transfer mechanism postulated for this heterojunction. TOC analysis revealed that the efficiency of Ag/1BI/1BW was 63 %, and reuse tests confirmed its high performance even after three cycles. This research provides new insights into the design of high-performance heterojunctions for water treatment.