Synthesis of a zinc-tungsten composite using a natural chelating agent for wastewater de-contamination.

Tannic acid (TA) is a cost-efficient and widely available plant-based chelator that can strongly bind to heavy metal ions through its polyphenolic groups. Thus, it is potentially a suitable and green substance for heavy metal decontamination of wastewater. However, TA is highly water-soluble and thus must be stabilized before use in water purification. In this context, the challenge is not only to stabilize or immobilize TA, but also to enhance its efficiency for removing heavy metals from aqueous solutions. To achieve this goal, we have produced a TA microplate incorporated with zinc-tungsten oxide nanoparticles (TA microplate-ZnWO4 NPs) via a convenient one-step hydrothermal process. Zinc and tungsten ions here act as effective cross-linking agents between TA polyphenolic groups, thereby reinforcing the TA microplate-ZnWO4 NPs composite during the hydrothermal process. We fully characterized this composite using XRD, FESEM, EDX, BET, XPS and FT-IR spectroscopy. As a proof-of-principle, we assessed its performance as an adsorbent for the removal of lead ions (Pb2+) from aqueous media. The removal percentage (RP) under optimal conditions was found to be 99.0% for 20.0 mg L-1 Pb2+ (pH = 6.0, adsorbent dosage = 10.0 mg, and contact time = 15 min). Also, the reusability test showed that this adsorbent maintains its performance over at least five additional adsorption-desorption cycles. Furthermore, we thoroughly investigated its adsorption mechanism and kinetics. This research confirms that our synthesized composite is an effective and promising candidate for use in water purification.