The effect of pHFigure 7 shows the result for the effect of pH, and the pHpzcof CCS was 6.8, as obtained from the curve. According to the literature, when the pH value of a solution is lower than pHpzc, the adsorbent surface is positively charged.26,32–34Otherwise, the adsorbent surface is negatively charged. As shown in Figure 1, SNE, which has sulfonic acid groups, is