Arsenic is universally recognized as a poison. The water-soluble form AsO43- is also very dangerous and can contaminate drinking water. If too much arsenate is consumed it can cause symptoms such as vomiting, abdominal pain, diarrhea, dehydration, and death which can occur even at very low concentrations. Although arsenic levels are monitored, many parts of the world are exceeding the recommended limit, and concentrations of arsenate are in danger of rising due to phosphate recycling. Phosphorus and phosphate are very important for agriculture. However, phosphorus is a non-renewable resource and mining for it is difficult and expensive. Instead, phosphate is recycled from water run-off so that it can be reused, but this process also recycles arsenate because they are very chemically similar. Their only difference is the central element. Both are in the same family on the periodic table, allowing them to participate in the same chemical reactions such as phosphate recycling. If recycling continues, arsenate concentrations will likely increase in drinking water and in fertilizers, which could poison human and plant life in the surrounding areas. This issue can be addressed with a probe that can selectively bind with arsenate. The probe utilizes hard/soft acid-base theory to modify the ligand’s selectivity so that it reacts with arsenate but not phosphate. The probe contains a lanthanide metal complex where the lanthanide acts as a hard Lewis acid which will bind well with hard anions like arsenate. Previous research has shown that the affinity of the probe for anions increases as the steric hindrance of the ligand around the metal decreases. The fluorescence and phosphorescence response of the probe can be used for the detection of the binding and study of the selectivity of arsenate. This fully developed probe can be modified and used to safely remove the deadly poison, providing clean drinking water and a more efficient recycle of phosphate.

Analyzing the affinity of a lanthanide metal complex probe to remove arsenate from drinking water

ACS Spring 2022

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