In
this study, we tried to synthesize lanthanum organic frameworks
(MOFs) with the linkers of benzoic acid (BA), 1,4-benzene dicarboxylic
acid, and 1,3,5-benzenetricarboxylic acid (BTC), abbreviated as La-BA,
La-BDC, and La-BTC, respectively. Interestingly, the BA linker approached
La metal to form lanthanum methanoate (La(HCOO)3) instead
of the La-BA MOF through an acid catalyst amide-hydrolysis mechanism,
whereas La-BDC and La-BTC act as MOFs, confirmed by PXRD patterns.
Various sophisticated instrumentation techniques such as FTIR, PXRD,
XPS, BET, and TGA were utilized to understand the formation of MOF.
This is the first report to investigate AsO4
3– adsorption and the dissolution behavior of La-BA, La-BDC, and La-BTC
in detail using different spectroscopic methods. The maximum AsO4
3– adsorption densities obtained from the
Langmuir isotherm model were found to be 2.623, 3.891, and 0.280 mmol/g
for La-BA, La-BDC, and La-BTC, respectively, where the dose ratio
was 1 g/L with the speed of 100 rpm at room temperature. The value
for La-BDC was significantly superior to the previously reported adsorbents
for AsO4
3– to date. The presence of AsO4
3– on both La-BA and La-BDC was confirmed
by FTIR and XPS As 3d. After adsorption of 2.4 mM AsO4
3–, the precipitation mechanism controls the adsorption
capacities on La-BA and the ligand exchange mechanism on La-BDC confirmed
by solution as well as solid analyses. Sorption kinetic data of AsO4
3– followed a pseudo-second-order model,
which is consistent with chemisorption involving the possible coordination
of AsO4
3– on La-BA and La-BDC. These
results suggested that the MOF materials can be developed to immobilize
arsenic-rich wastewater.
