Tungsten oxide (WO3) is an exceptional semiconductor that exhibits absorption within the visible region of the solar spectrum, and it is completely feasible to use it in different applications. Several studies have reported its use in the photocatalytic degradation of organic matter such as methylene blue, rhodamine B, methyl orange, etc. However, the photocatalytic behavior of WO3 is limited because the edge of its conduction band is below of the position for the single-electron reduction of O2.

Herein, an efficient and stable WO3 based photocatalyst (WO3/g-C3N4) from ammonium paratungstate (APT) for degradation of Orange G dye and ciprofloxacin antibiotic under solar light. the WO3/g-C3N4 is produced by an ultrasound-assisted method. 

Preparation method of WO3/g-C3N4 composite material is as follows:

The graphitic carbon nitride, g-C3N4, was prepared by polycondensation of tris-s-triazine units through the calcination of melamine at 500 °C for 4 h. The reaction yield after the heating process was approximately 50%. The WO3 powder was obtained by means of an ultrasound-assisted technique. First, 1.10 g of ammonium paratungstate (APT, 99.99%)was dissolved in a dilute aqueous solution of nitric acid (10% v/v). Afterwards, the suspension obtained was placed in an ultrasound equipment (Fisherbrand, FB11201) for 2 h. Subsequently, the solution was heating at 90 °C for 12 h under stirring conditions to provide the evaporation of the solvent. Finally, the obtained powder was calcined at 500 °C for 4 h.

The hybrid WO3/g-C3N4 system was prepared at several amounts of tungsten oxide, i.e. 1, 3, 5, 7 and 10 wt.%. In this regard, different amounts of WO3 and g-C3N4 were added to an ethanol-water solution 50% v/v. The resulting slurry was stirred at 60 °C for 15 min. After the stirring process, the mixture was subjected to ultrasonic treatment at 37 kHz for 1 h to eliminate agglomerates and favoring the interaction between the particles of both semiconductors. Then, the suspension was dried in an oven at 90 °C under static conditions. The resulting powder was ground in an agate mortar and stored under moisture-free conditions.

In summary, an efficient and stable WO3 based photocatalyst (WO3/g-C3N4) from ammonium paratungstate (APT) for degradation of Orange G dye and ciprofloxacin antibiotic under solar light. The highest photocatalytic activity was achieved by the sample containing 5 wt.% WO3. The photocatalytic performance of the obtained composites was examined by the photodegradation of the Orange G dye as well as the ciprofloxacin antibiotic. This improved photocatalytic behavior can be attributed to the heterojunction formed between both semiconductors, leading to a decrease in the recombination of the photogenerated hole-electron pairs, and thus, an increase in the formation of reactive oxygen species. The role of the reactive species was elucidated during the photodegradation of the pollutants. For Orange G dye, it was evident that the superoxide ions play the main role due to the high participation of this reactive oxygen species in the two possible mechanisms of photodegradation of a dye, as mentioned above. On the other hand, the photogenerated holes in the photocatalyst yielded the predominant role as a direct oxidation of the ciprofloxacin antibiotic. In addition, the WO3/g-C3N4 system exhibited a sustained photoactive performance after three consecutive cycles of degradation of the Orange G dye.