Virus Filtration by Nanodiamond Modified Membranes

At least 1 billion people lack access to safe water due to rapid population growth, urbanization, industrialisation and the climate emergency. One of the biggest challenges to water purification is the removal of harmful nanoscale contaminants such as viruses and industrial contaminants such as dyes and pharmaceutical by-products. Of the existing filtration platforms, only nanofiltration or reverse osmosis can achieve high retention levels of such nanoscale pathogens. These systems are expensive and complex, being mostly limited to centralised water treatment systems. This has led to the development of adsorptive depth filtration (ADF) where contaminants are targeted by van der Waals / electrostatics forces, hydrophobic interactions etc driving contaminant adsorption to the membrane surface. A key advantage of such a technology is that retention is not achieved through size exclusion, allowing much higher flow rates and smaller pressure differentials.<br/>In this work¹, quartz filters are modified with hydrogenated diamond nanoparticles, reversing the zeta potential of the membranes from negative to positive across a wide pH range. Untreated quartz filters demonstrate log0.2 (35%) retention of viruses (MS2 bacteriophage) whereas the diamond modified ones exhibit at least log6.2 (&gt;99.9999%) reduction from feed waters. This is due to the overwhelming majority of viruses exhibiting a negative zeta potential in water and thus being attracted to the positively charged diamond modified membrane. The modified membrane was also tested with far smaller contaminants such as acid black 2 dye and demonstrated &gt;90% higher retention over the unmodified filter. Finally, the diamond modified filter was compared to the incumbent alumina-based technology where it demonstrated a consistently higher positive zeta potential over a larger pH range. Thus, diamond modified filters offer higher zeta potentials vs pH and thus higher virus retention over current ADF technologies.<br/>¹ H.A. Bland, ACS Appl. Nano Mater. <b>4</b>, 3252 (2021).