a, Pb-sequestering performance as a function of soaking time for DMDP films coated on glass substrates. The DMDP film thicknesses are indicated. All DMDP films are soaked in 50 ml of 1.93 × 10−5 M PbI 2 aqueous solution (equivalent to 4 ppm of Pb2+) to test their Pb-absorbing capability. Five samples were measured for 2.36-μm-thick DMDP and three samples were measured for other DMDP film thickness, with the averages and standard deviations (error bars) indicated. b, Evaluation of Pb-sequestering capabilities of different EDTMP-blended films prepared by various methods. Three samples of each configuration type were measured with the averages and standard deviations (error bars) indicated. The films were soaked in 50 ml of aqueous PbI 2 solution with a Pb concentration of 7 ppm. ‘5% PEO in water’ stands for the film prepared by dissolving 5 wt% PEO (viscosity-average molecular weight, about 2,000,000) in pure water as solvent, followed by adding a proper amount of EDTMP under stirring. Then the mixture was smeared into a thin film using a doctor-blade coating method with such an area that the concentration of EDTMP is 0.01 g cm−2. ACN was used as the test solvent. PVA, polyvinyl alcohol (molecular weight 86,000).