Opportunity
The presence of heavy metal ions (HMIs) such as lead, cadmium, and mercury in drinking water poses a severe threat to human health due to their high toxicity, mobility, and non-biodegradability. Existing technologies for removing these metal ions, including chemical precipitation, solvent extraction, ion exchange, and membrane separation, often fail to meet the stringent World Health Organization (WHO) limits for drinking water (e.g., 10 ppb for lead, 3 ppb for cadmium, and 6 ppb for mercury). Adsorption methods, while promising due to their high capacity, selectivity, and operational simplicity, face significant challenges when implemented with common two-dimensional (2D) materials like hexagonal boron nitride (h-BN), graphene oxide (GO), MXenes, and conventional transition metal dichalcogenides (TMDs). These challenges include weak adsorption affinity, low selectivity, slow adsorption kinetics, and an inability to reduce residual lead ion concentrations to below the critical WHO threshold. Consequently, there is a pressing need for an improved method and apparatus capable of efficiently reducing metal cation concentrations in fluids, particularly in drinking water, to levels that comply with international safety standards.
Technology
This patent addresses the existing problem by introducing a novel filtration method and apparatus utilizing a specialized membrane. The core innovation lies in the membrane's composition: it comprises a polymer substrate (e.g., nylon or polyvinylidene fluoride, PVDF) upon which multiple layers of 1T/1T′-phase transition metal dichalcogenide (TMD) nanosheets are deposited. These nanosheets, such as 1T′-MoS₂, 1T′-WS₂, 1T-TaS₂, or 1T-TiS₂, are synthesized via a specific electrochemical lithium-intercalation and exfoliation process. This process involves discharging a lithium battery with a TMD bulk cathode to create lithiated TMD, followed by ultrasonication in water to exfoliate it into metallic-phase (1T/1T′) nanosheets, which are then collected, dispersed, and vacuum-filtered onto the polymer substrate. The resulting membrane leverages the unique properties of these 1T/1T′-TMD nanosheets, which possess a metallic character and negative surface charge, enabling exceptionally strong and selective adsorption of metal cations, especially lead ions (Pb²⁺). The technology demonstrates that this membrane can effectively reduce the concentration of metal cations in a fluid from an initial 2 parts per million (ppm) to below 10 parts per billion (ppb), thereby directly meeting the WHO guideline for lead.
Advantages
- Achieves ultra-low residual concentrations, reducing Pb²⁺ from 2 ppm to below 10 ppb, meeting strict WHO drinking water standards.
- Exhibits exceptionally high adsorption capacity for lead ions, ranging from 175 to 530 mg/g depending on the TMD type (e.g., ~530 mg/g for 1T′-MoS₂).
- Demonstrates superior selectivity for toxic heavy metals (e.g., Pb²⁺, Cu²⁺) over common background ions (e.g., Na⁺, K⁺, Ca²⁺, Mg²⁺), with distribution coefficient (K_d) values for Pb²⁺ 2-4 orders of magnitude higher.
- Features rapid adsorption kinetics, achieving reduction to <10 ppb within 1 to 4 minutes for various TMD nanosheets.
- Enables membrane regeneration and reuse through washing with chelating agents like EDTA, maintaining high removal efficiency (>92%) over multiple cycles.
- Shows excellent stability across a wide pH range (0-14) and long-term aqueous environments without structural degradation or detachment from the substrate.
- The fabrication method using electrochemical exfoliation is scalable and yields high-purity, monolayer/bilayer nanosheets with high yield (>92%).
Applications
- Point-of-use (POU) and point-of-entry (POE) water purification devices for household drinking water.
- Portable water filters for emergency response, travel, or outdoor activities.
- Industrial wastewater treatment systems for removing heavy metals from effluents.
- Integration into municipal water treatment plants for advanced polishing stages.
- Remediation of groundwater and contaminated water sources.
- Selective recovery of valuable metals (e.g., copper, nickel) from process streams.
- Development of specialized filtration cartridges for aquariums or laboratory use.
