CuO/CuWo4 Heterostructure Obtained via Sol-Gel Method from Ammonium Paratungstate

Several studies reported that modifying CuO with CuWO4 can increase its photoactivity. Sodium tungstate dihydrate (Na2WO4·2H2O) is the most commonly-used metal salt precursor for tungsten, whereas compounds such as ammonium paratungstate (APT) have rarely been explored.

A sol-gel process to fabricate  CuO/CuWO4 photocatalysts have been conducted using APT as a starting material.

The synthesis process can be concluded as below:

First, 27.7012 g of pure copper (II) nitrate 3-hydrate pure (Cu(NO3)2·3H2O 98–103 %) was entirely solubilized in 17 mL of ethanol (C2H5OH 96 %) and 2.8895 g of ammonium paratungstate (APT, 99 %) was entirely solubilized in 5 mL of distilled water. After 6 h, both solutions were mixed, and the pH value was recorded (pH = 2). This final solution was evaporated for 30 min at 50 °C to form a gel. A thermic process in a Vulcan 3–1750 oven at 120 V and 50/60 Hz was used to stabilize the gel; this was submitted at 200 °C at a rate of 1 °C/min for 4 h. The resulting material was ground in an Agata mortar. The final materials were thermally treated in a Terrigeno D8-2471 oven at 220 V in air and exposed to 300 °C, 500 °C, and 700 °C at a rate of 1 °C/min for 4 h and 900 °C divided into two stages: 300 °C at 1 °C/min for 2 h, and 900 °C at 2 °C/min for 4 h. CuO was synthesized and crystallized at 500 °C for comparison purposes (without adding ammonium paratungstate).

In conclusion, it was proved that using ammonium paratungstate to synthesize copper-tungsten materials through the sol-gel process promotes the formation of CuO/CuWO4 heterostructure materials. Results showed that 300 °C was the optimal temperature for forming the CuO/CuWO4 heterostructure. The synthesized materials at 300 °C had an optical band gap of 2.66 eV (direct gap) and 1.35 eV and 2.11 eV (indirect gap), which were lower values than those of the CuO and CuWO4.

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