Suitability of Two Methods for Determination of Point of Zero Charge (PZC) of Adsorbents in Soils

The points of zero charge (PZC) of manganese oxide (MnO2), titanium dioxide (TiO2), aluminum (Al) laterite, ferruginous (Fe) laterite, aluminum oxide (Al2O3), and a commercial activated carbon sample (AC001) were determined using acid-base potentiometric (PT) and mass titration (MT). The MT technique has been used extensively for carbonaceous materials but less for soils. In addition, little work has been done on the PZC of these metal oxides and carbon materials under similar experimental conditions concurrently. Our aim is to buttress the ease of MT usage over PT in routine laboratory analysis. The experimental PZC measured by acid-base potentiometric and mass titrations respectively were 4.97 and 4.11 for MnO2; 5.38 and 5.74 for TiO2; 4.19 and 4.08 for Al laterite; and 4.45 and 4.10 for Fe laterite. For Al2O3 and activated carbon, mass titration gave 7.53 and 8.41 respectively. Calculated standard deviations between the means of PT and MT were less than 1, and Student's t-test at 95% confidence interval (CI) gave a P value of 0.135, suggesting that there is no significant difference between PT and MT and buttressing the reliability of the experimental procedures. In routine laboratory work, mass titration should be preferred for PZC measurement of (hydr)oxides and soil materials because it saves time.