A method of removing barium from a liquid includes adding a two-dimensional metal carbide water contaminant adsorbent to water to adsorb contaminants, such as barium (II), from the liquid. The two-dimensional metal carbide water contaminant adsorbent is in the form of at least one MXene, having the formula Mn+1Xn, where n=1, 2 or 3, M is an early transition metal, such as scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo) or the like, and X is either carbon or nitrogen. The MXene may be Ti3C2. The liquid may be, for example, at least one water by-product from at least one oilfield reservoir, such as produced water, co-produced water or a combination thereof.