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Khalifa University Researchers Use Synthesized Nanoparticles to Protect the Environment from Persistent Pollutants in Wastewater

To aid in the treatment of wastewater, researchers from Khalifa University have synthesized a nanostructured metal oxide material to kickstart a reaction aimed at removing phenol from wastewater 

Industrial wastewater is an undesirable by-product of various industrial processes and needs to be treated and cleaned before it can be reused or disposed of to prevent any environmental detrimental impact. Many pollutants can be very difficult to treat.

To aid in the treatment of wastewater, Dr. Mohammad Abu Haija, Assistant Professor of Chemistry, and Dr. Fawzi Banat, Chair of Chemical Engineering, have synthesized a nanostructured metal oxide material to kickstart a reaction to remove phenol from wastewater. They described their catalyst in a paper recently published in the journal Applied Catalysis B: Environmental.

“The wastewater typically produced during industrial processes contains organic and inorganic pollutants that are environmentally persistent and cannot be removed by conventional methods,” explained Dr. Banat. “Some of these pollutants are dyes, pesticides and organic solvents which may contain aromatic compounds, cyanides, ammonia, sulphides, and phenols.”

Phenol is a persistent organic pollutant that is commonly used in agriculture and in general disinfection.

“Phenol’s poor biodegradability demands a tertiary treatment as the conventional primary and secondary processes, like membrane technology and electrochemical processes, are not efficient at dealing with phenol in wastewater,” said Dr. Haija.

Recent studies have indicated an increase in the prospect of advanced oxidation processes focused on peroxymonosulfate (PMS) activation as an effective treatment method, owing to its pH flexibility, redox potential and great oxidation ability.

“The use of PMS as an oxidant has attracted a lot of attention due to the different reactive oxygen species produced during its activation process,” explained Dr. Haija.

However, PMS alone is not enough to take care of the phenol in wastewater. It needs a catalyst to get the degradation reaction started.

Activation via metal oxide catalysts has drawn much attention as they are reusable, easy to recover, and reduce the need for chemical reagents. Even though the naturally abundant transition metals show high activation of PMS, their high solubility and toxicity make them somewhat unfavorable for use in wastewater treatment and other environmentally focused applications.

Metal oxides with vanadate (a salt containing both vanadium, a transition metal, and oxygen) are environmentally abundant oxides, with remarkable physical and chemical properties which enable their application in batteries, semiconductors, and catalysis. Combining vanadate with rare earth metals such as cerium, lanthanum and praseodymium shows a great enhancement in their electrochemical properties, thermal stability, surface area and magnetic properties.

Cerium vanadate (CeVO4) is naturally occurring and can also be prepared using simple methods in the laboratory.

“Due to its optical, electrical, magnetic and catalytic properties, CeVO4 is often used as a catalyst, with several reports about its efficiency at degrading organic pollutants, such as organic dyes and for the oxidative dehydrogenation of propane,” explained Dr. Banat.

The research team at KU prepared CeVO4 nanoparticles using a simple ‘one-pot’ co-precipitation method. The prepared nanoparticles were scrutinized for their stability and purity and were found to exhibit good crystallinity and display a rod-like structure. The lab-derived CeVO4 replicated naturally occurring cerium vanadate.

The crystalline structure of pristine CeVO4 nanostructures as shown in various tests: (a) XRD pattern, (b) Crystal structure, (c) Raman spectrum and (d) FTIR spectrum

The lab-derived CeVO4 was then used to activate PMS for phenol degradation experiments. To prove that the catalyst was responsible for the results, the researchers also ran experiments where they removed the catalyst from the reaction system. They saw that negligible phenol degradation was achieved, which shows that the reaction is completely derived by the catalyst.

“We conducted preliminary experiments using PMS alone, CeVO4 alone, and then CeVO4 with PMS,” said Dr. Banat. “To emphasize the importance of the catalyst performance, we tested the self-adsorption of the catalyst and the self-oxidation of PMS first. We found that PMS alone was not effective at degrading phenol, as only 2 percent of phenol was removed after about 180 minutes. CeVO4 alone was also insufficient, removing less than 20 percent of phenol in 180. Remarkably, PMS and CeVO4 combined achieved a complete degradation of phenol within 80 minutes, suggesting the PMS was activated by the CeVO4 catalyst.”

The system has uses beyond just phenol degradation too.

To investigate the CeVO4and PMS system for use in degrading different organic pollutants, the researchers tested organic pollutants, including resorcinol, acrylamide, methyl violet and methyl, with the system. The results showed that the CeVO4/PMS system successfully degraded all four organic pollutants.

Plus, the CeVO4 nanoparticles were found to be reusable.

“The regeneration and reusability of a catalyst are important criteria for any practical application,” explained Dr. Haija. “Our regenerated CeVO4 nanoparticles were tested for five consecutive cycles using the same reaction parameters. Our results showed that the reused catalyst exhibited high catalytic activity, proven by the complete degradation of phenol within 60 minutes. Plus, there was no significant leaching of either cerium or vanadate from the catalyst.”

“Combining a simple synthesis method with the excellent catalytic properties exhibited by CeVO4 is a suitably cost-effective and environmentally friendly technique that can be employed in water treatment applications.”

Jade Sterling
News and Features Writer
26 March 2020