Zinc oxide – mesoporous silica nanocomposite: preparation, characterisation and application in water treatment for lead, cadmium and chromium removal

Figures & data

Figure 1. XRD pattern for ZnO-NP (bottom) and ZnO-mSiO₂ nano-composite (top).

Two XRD patterns for comparison, showing that the zinc oxide mesoporous silica has features of both nano zinc oxide and silica.

Figure 2. TGA data for the ZnO-NP (a), and ZnO–mSiO₂ (b) samples.

TGA plots showing differences between zinc oxide nanoparticles and the zinc oxide silica composite; the zinc oxide loses little mass across the temperature range whereas the composite loses more than 30%.

Figure 3. Nitrogen adsorption-desorption isotherm for ZnO-mSiO₂ and the pore size distribution (insert).

BET data showing nitrogen adsorption and desorption across a range of applied relative pressures, with an inset that shows dominant pore width, for the composite material.

Table 1. The pore volume and surface area data obtained for mSiO₂, Zn-NP and ZnO-mSiO_2..

Material	Surface area (m^2 g^−1)	Pore volume (cm^3 g^−1)
mSiO2	637	0.640
ZnO-NP	54	0.071
ZnO-mSiO2	155	0.154

Figure 4. Effect of pH on Pb (II), Cd (II) and Cr(III) adsorption (% removal from solution), with initial solution concentration 100 mg/L, 25 mg sorbent, 25 mL solution volume and 3 h equilibration time.

Scatter and line plot showing percentage of cadmium, chromium and lead removal via adsorption by the different test materials across a pH range; greater than 80% removal occurred in all cases at pH 7 and above.

Figure 5. Effect of contact time on Pb (II), Cd (II) and Cr(III) removal percentage at pH 7, initial concentration 100 mg/l, 25 mg sorbent and 25 mL total volume.

Scatter and line plot showing percentage of cadmium, chromium and lead removal via adsorption by the different test materials across a range of contact times; approximately 80% removal occurred in all cases at 90 minutes and above.

Figure 6. Effect of adsorbent dose on a) removal efficiency and b) amount sorbed (mg/g) of Pb (II), Cd (II) and Cr (III) with conditions set at pH 7, temperature 25°C, total volume 25 ml, and initial Pb, Cd and Cr concentration 100 mg/L.

Two scatter and line plots showing percentage of metals removed and adsorbed by the tested materials when the ratio of sorbent mass to solution volume was varied.

Figure 7. Effect of initial concentration of Pb (II), Cd (II) and Cr(III) on removal percentage by the adsorbents with conditions set at pH 7, temperature 25°C and sorbent dose 25 mg : 25 ml solution.

Line and scatter plot of percentage cadmium, chromium and lead removed by the tested materials as a function of initial solution concentration.

Table 2. Freundlich and Langmuir linear isotherm model parameters and equations.

Freundlich	Line equation	R^2	1/n	KF
Pb_ZnO	y = 0.4272x + 1.5233	R^2 = 0.9907	0.4272	33.366
Pb_ZnO-mSiO2	y = 0.4575x + 1.6555	R^2 = 0.9837	0.4575	45.238
Cd_ZnO	y = 0.7186x + 0.9053	R^2 = 0.9912	0.7186	8.041
Cd_ZnO-mSiO2	y = 0.7493x + 1.02	R^2 = 0.9911	0.7493	10.471
Cr_ZnO	y = 0.5275x + 1.3208	R^2 = 0.9669	0.5275	20.931
Cr_ZnO-mSiO2	y = 0.5361x + 1.5764	R^2 = 0.9913	0.5361	37.705
Langmuir	Line equation	R^2	qm, (mg/g)	KL (L/mg)
Pb_ZnO	y = 0.0103x + 0.0159	R^2 = 0.9647	97.1	0.65
Pb_ZnO-mSiO2	y = 0.0097x + 0.0081	R^2 = 0.9822	103.1	1.20
Cd_ZnO	y = 0.0081x + 0.1384	R^2 = 0.9916	123.5	0.06
Cd_ZnO-mSiO2	y = 0.0068x + 0.0964	R^2 = 0.9943	147.1	0.07
Cr_ZnO	y = 0.0103x + 0.0365	R^2 = 0.9506	97.1	0.28
Cr_ZnO-mSiO2	y = 0.0089x + 0.0135	R^2 = 0.9775	112.4	0.66