Novel Catalytic Membrane Boosts Wastewater Treatment Efficiency

The novel technology uses modified advanced oxidation process (AOP) to target phenolic pollutants in wastewater, such as those produced by the oil and gas industries. The technology was developed by a research team at Hong Kong Baptist University.

Why do we need to target phenolic pollutants in wastewater?
Phenolic compounds are a major group of organic pollutants that can have serious detrimental effects on humans, animal life, marine life, and agricultural production. They are produced by various industries, such as the petrochemical manufacture, oil refineries, coal mining, but also in effluent from pharmaceutical, textile, coal gasification, leather, resin synthesis, pulp and paper, paint, and wood processing.

They can persist in the environment for a long time and pose a significant threat to rivers, lakes, reservoirs, and even drinking water supplies.

Traditional methods of removing phenol compounds from wastewater require hazardous chemicals and/or energy-intensive processes.

Novel technology utilising advanced oxidation processes
The process makes use of AOPs, which have been developed and used for some years to remove pollutants and contaminants from water. The process involves activating oxidants to turn them into reactive oxygen species (ROS), which then break down the pollutants. When it comes to targeting phenolic compounds, one ROS is particularly effective – singlet oxygen.

AOPs have been increasingly recognised and developed over the past few decades to remove pollutants from water. They are a set of chemical treatment methods which activate oxidants into reactive oxygen species (ROS) that can be used to break down pollutants in wastewater. Among these ROS, singlet oxygen (1O2) is particularly effective in targeting phenolic compounds.

Singlet oxygen, or dioxidene, is molecular oxygen in an excited state which gives it high energy and electrophilic properties. It can be found in nature and has traditionally been used for chemical syntheses and medical techniques. However, its properties are being recognised for their potential use in environmental remediation, such as in breaking down phenol compounds.

Overcoming barriers to using AOP
Creating ROS for wastewater treatment processes usually requires high energy use and the need for strong oxidants. The researchers at Hong Kong Baptist University attempted to address these issues, along with two further barriers to using AOP: The inefficient transfer of molecular oxygen (O2) in water due to its low solubility; and the difficulty in getting pollutants to interact with the catalyst surface due to the surrounding water film as a barrier.

Developing a new membrane
The team, led by Professor Zhao Jun, associate professor of the Department of Biology, overcame these barriers by developing a novel catalytic membrane, which they named ‘NGCF-OV’.

The membrane is made from a composite that combines two advanced materials: N-doped reduced graphene oxide; and cobalt ferrite. As well as tackling the above barriers, it also addresses the challenge of efficiently activating molecular oxygen to become singlet oxygen.

Professor Zhao told local media: “This research marks a significant advancement in the field of water treatment and represents a promising strategy for addressing environmental pollution. By effectively integrating the processes of oxygen activation and pollutant degradation within a single membrane, this technology offers a more sustainable and efficient approach to treating contaminated water.”

How does the membrane work?
Essentially, the membrane contains unique sites that can adjust the bond length of oxygen (O2), or the distance between the centers of the two oxygen atoms that are bonded together. According to the research team, this facilitates faster and more efficient electron transfer, which means singlet oxygen can be created without the need for external energy and catalytic agents.

The membrane serves a dual purpose because it also features graphitic nitrogen sites that trap pollutants close to the membrane’s surface. This overcomes water film barrier issues because the distance between the singlet oxygen and the phenol compound pollutants is significantly reduced.

In testing, the membrane demonstrated superior efficiency in generating and utilizing singlet oxygen for pollutant degradation. Test results show that this novel technology can completely degrade bisphenol A, a common and harmful pollutant, in just 86 milliseconds (one thousandth of a second), outperforming many existing cleanup methods.

Applications beyond phenol destruction
Application of the membrane is not limited to the degradation of phenol compounds, like bisphenol A. Its catalytic properties can be applied to a wide variety of organic pollutants in wastewater, such as antibiotics, pesticides, and dyes.

Zhao added: “The ability to generate reactive oxygen species without external energy inputs makes this membrane particularly suitable for emergency pollution remediation and everyday water treatment applications.”