Something I do not understand: you "filtered" soluble salts (buffer, SDS)? What was the purpose? I suppose that you see dried mixture of salts on your filter. Surely, EDS can help (if your SEM equipped with one).

Dear Makayla,

the fast method is that you try to use FTIR for your so-called fouled membrane, reference membrane and dried SDS and see if you see new peaks or any obervable changes. About EDS, as both PES and SDS have a Sulfur element (S) in their structure and considering the higher energy needed for EDS measurements, then it might be a bit confusing however you can try.

@Mohammadamin Esmaeili

Thank you for the answer. One Question: can I use FTIR to quantify the fouling? Im not sure if FTIR is only for determining the bonds in a material?

For EDS, do u think the high energy will damage the sample ? I dont know which method is better to use? Thanks

Dear Makayla,

I am not sure if you can quantify the amount of fouling based on FTIR alone. But let's discuss your issue a bit and hope I get your point. for any analytical analysis, we need a calibration standard. Let's assume you have a known feed solution concentration and you are using cross-flow flow filtration, after you stop the filtration, the concentration of your concentrate and permeate can be determined, so assuming the rest caused fouling. Remember that the volume of your initial feed, and permeate and concentrate are important to verify the mass balance. At this point, you can assume that the fouling occuoccurredcross-flowred evenly and calculate the amount of foulant per area of the membrane.

Another method is also, to cut 3 pieces (known area) of the fouled membrane, and then put that in 3 separate glass tubes (triplicate) and add a known amount of solvent that can dissolve your foulant. Afterwards, use an analytical instrument that can determine the concentration of your foulant which you can easily convert to gr based on the known added volume to the tube. Calculate the average and divide per area.

Last but not least, you can start with different known concentrations of sodium dodecyl sulfate in buffer solutions and do the same procedure that I explained and further also use FTIR and connect the concentration to the intensity or area under specific peaks if the peak is specific to your foulant and not the membrane. Now you can have a calibration curve that connects the ftir and concentration of foulant per area of the membrane. Just remember the time of filtration and pressure, temperature, flow velocity, (turbulent flow), pH and other important factors should be constant.

In the case of real-time monitoring of fouling using Raman spectroscopy, you can read the article of my colleague and maybe get some hints.

https://www.sciencedirect.com/science/article/abs/pii/S0376738816316817

In one of my papers, I was also trying to identify the amount of vanillin adsorbed on the membrane surface after my experiment and I explained the methods there, which is similar to what I have learned from my colleague in the abovementioned article.

https://www.mdpi.com/2077-0375/9/4/56/htm

Hope my explanation is clear and I got your point correctly.