Toward an Accurate Spectrophotometric Evaluation of the Efficiencies of Photocatalysts in Processes Involving Their Separation Using Nylon Membranes

Abstract

Many works include the use of nylon membranes to separate the solid particles of photocatalysts from the photocatalytic reactors, before using spectrophotometers to evaluate the catalysts' performance in the photocatalytic degradation of many pollutants. This might lead to significant errors due to the adsorption of some pollutants within the structure of the membranes during the filtration process used to separate the solid particles of the photocatalysts to get a clear filtrate. This, consequently, leads to incorrect calculations, which in turn are translated into false high photocatalytic efficiencies of the used catalysts. In this work, the authors study the interaction between nylon membrane filters and five different model compounds-phenol red, methylene blue, rhodamine B, rhodamine 6G, and phenol. The study reveals a significant interaction between the nylon membranes and both rhodamine B and phenol red.During the investigation of the fluorescence signal in the photodegradation of polymers and pollutant degradation, we serendipitously discovered that a simple model compound, such as phenol red and rhodamine B, is removed efficiently through filtration using the commonly used Whatman nylon filter membranes purchased from Sigma Aldrich. This type of filter membrane, with a 0.2 µm pore size, 47 mm diameter, and 0.5 mm thickness, is proposed to be used after the photodegradation process to remove the submicron photocatalysts and obtain the filtrate for spectrophotometric analysis. This observation made us curious and, thus, we decided to investigate more in depth the removal efficiency of these nylon membranes and the removal mechanism beyond this observation. We chose several probes with different chemical characteristics, such as rhodamine B, phenol, rhodamine 6G, phenol red, and methylene blue. Our results indicate that the nature of the chemical structure is responsible for the removal through a chemical mechanism, involving a negatively charged molecule interacting with a positive charge from the terminal part of a polymer backbone in polyamide-based filters.

Eco-friendly highly efficient BN/rGO/TiO2 nanocomposite visible-light photocatalyst for phenol mineralization

“…The samples were drawn from the reaction vessel every 5 min and filtered using a nylon filter paper of pore size 0.4 μm. It is good to note that no phenol elimination was observed using the mentioned nylon filter paper, as demonstrated earlier (Al-Kandari et al 2018 ). The progress of the photocatalytic reaction was monitored using a UV - Vis spectrophotometer in the range of 190–400 nm, with 279 nm corresponding to the highest absorption of phenol.…”

CE-UV/LIF Analysis of Organic Fluorescent Dyes for Detection of Nanoplastics in Water Quality Testing

“…Conversely, as depicted in Figure 13b, incrementing the mass of nanospheres further (from 10 to 350 µg) inversely affects the % binding. This counterintuitive result is interpreted as the onset of nanoparticle aggregation when in high concentration within the 1.6 mL water sample [63]. Aggregation reduces the effective surface area available for R6G binding, since clusters of nanospheres offer fewer exposed binding sites compared to 0.0 0.5 the same mass of dispersed nanoparticles.…”