Drilling of microhole array on aluminum foil by nanosecond laser pulses and its application in oil-water separation

In this work, we report the drilling of microhole arrays on a pure aluminum foil of 50 μm thickness using a 200 W average power nanosecond pulsed fiber laser. Holes were made by trepanning with six different pulses of varying duration from 29 to 2020 ns. The surface morphology of the wall of the holes was studied using a scanning electron microscope and was found to be different for holes made with different optical pulses. Laser induced periodic surface structures were found to be generated when the hole was drilled by optical pulses of 29 and 53 ns durations. These laser induced structures were found to be responsible for altering the wettability of the hole walls, thereby making the hole walls suitable for use as filters to separate oil and water from oil-water mixture. The filtration ability of these microhole arrays in separating oil-water mixture was assessed, and the separation efficiency of the filters made with 29 and 53 ns optical pulses having a hole diameter of ∼55 μm was found to be ∼99%. The laser processed array of holes showed switchable wettability. The purity of the filtered water was tested by Fourier transformed infrared spectroscopy.