Development of chitosan doped by TiO2/polyoxomolybdate nanophotocatalyst for photocatalytic degradation of Ephedrine and Pseudoephedrine in clandestine wastewater

Different approaches such as delivery to chemical waste management facilities, recycling/reusing, burning into the open air, burying under the soil and sea, burying in the rivers and other waterways, burying in remote areas, releasing into the urban sewage system, and evaporation were frequently used for destruction of illicit drugs, which were selected according to the conditions and facilities. Environmental problems have called the alarm for the human community. Developments of new environmentally friendly, sustainable and effective energy technologies are inevitable. Removal of chemical wastes is one of the most important goals to protect human health and environment. Since the introduction of some chemical wastes into the water resources can cause irreversible damage to humans and other organisms, removing these pollutants from water is one of the most important activities of countries. One of the new methods for the destruction of chemical wastes is photodegradation using photocatalysts in the presence of sunlight as a clean, inexpensive, and powerful light source [1,2].There are many synthetic routes used in clandestine laboratories to produce amphetamines. Ephedrine and pseudoephedrine have been common precursors in the reactions, and the Leuckart reaction and the Birch method are well-known synthetic routes.The purpose of this study is to destroy of ephedrine and pseudoephedrine using photodegradation technique. For this purpose, chitosan doped by TiO2/polyoxomolybdate nanophotocatalyst was synthesized for photocatalytic degradation of ephedrine and pseudoephedrine in clandestine wastewater. This nanophotocatalyst was prepared by sol–gel method and characterized through FT-IR spectroscopy, SEM-EDX, thermogravimetric (TG) and XRD analyses. In the experimental part, the destruction of ephedrine and pseudoephedrine were studied in photocatalytic degradation on a stainless-steel mesh coated with nanocomposite of chitosan, titanium dioxide and polyoxomolybdate (CS/TiO2/PMO12). In order to achieve the best photodegradation efficiency, sample volume per each experiment, pH, ephedrine and pseudoephedrine concentration, temperature and the percentage of photocatalysts, were studied. CS/TiO2/PMO12 nanocomposite is a cheap photocatalyst, non-toxic, with a simple preparation method, could destroy ephedrine and pseudoephedrine with high degradation efficiency. Titanium dioxide is a powerful photocatalyst that has been enhanced with compositing and doping, successfully eliminated amphetamine which is a tough chemically degradable drug. Polyoxometalates (POMs) have been studied as a green and cheap photocatalyst for the removal of organic pollutants or transition metal ions from water. POMs, which have similar light absorption and electrochemical band-edge positions to those of TiO2, are a large variety of oxygen-bridged metal clusters with unique structural characteristics and rich photocatalytic action. The composites showed higher photocatalytic activity than pure TiO2 or pure POMs. The results show that the POMs could be dispersed better in TiO2 substrate by sol–gel method than by incipient wetness method; the CS/TiO2/PMO12 nanocomposite prepared by sol–gel method had a higher photoactivity performance; moreover the reaction was dependent on POMs loading. The efficiency of photocatalytic process was evaluated with GC-FID and GC-MS analyses. The life time experiment for one coated steel mesh showed no significant loss in performance of composite coating over 20 times of photodegradation owing to the high chemical stability of CS/TiO2/PMO12 nanocomposite. The thermal and mechanical stability of the prepared nanomaterial and the high relative recovery make this nanophotocatalysts superior to conventional photocatalyst for degradation of ephedrine and pseudoephedrine in clandestine wastewater.

Keywords:

Nanophotocatalyst , Clandestine wastewater , CS/TiO2/PMO12 nanocomposite , Photocatalytic degradation