A recyclable MOF@polymer thin film composite for nanomolar on-site fluorometric detection of heavy metal ion and anti-histamine drug and efficient heterogeneous catalysis of Friedel–Crafts alkylation

Abstract

Developing a robust, reliable, fast-detecting sensor is a significant challenge for present-day researchers. Hence, a dual-functional fluorometric sensor was designed to detect heavy metal ions (e.g., Hg²⁺) and anti-histamine drugs (e.g., ranitidine) at the nanomolar level in the aqueous medium. A stable and efficient thiourea-functionalized aluminum−based metal-organic framework (MOF) was prepared and its guest-free form was applied for the selective detection of the above-mentioned analytes with a low detection limit (Hg²⁺ = 7.3 nM and ranitidine = 3.4 nM). The MOF was exceptionally sensitive to Hg²⁺ and ranitidine detection with a fast response time of 10 s and 5 s, respectively. Our probe has the highest K_SV values for these targeted analytes among the sensors documented to date (i.e., 1.29 × 10⁶ M⁻¹ for Hg²⁺ and 7.99 × 10⁵ M⁻¹ for ranitidine). This work reports the first MOF-based sensor for ranitidine detection. About 93% and 98% fluorescence quenching was observed after introducing Hg²⁺ and ranitidine, respectively. The probe has excellent selectivity toward detecting Hg²⁺ and ranitidine, even in the presence of interfering analytes. The sensing capability of the probe was explored in different media, including serum, urine, wastewater, different pH, etc., which indicates the real-field applicability of the sensor. A cost-effective, highly efficient, long-lasting MOF@polymer thin-film composite (MOF@PVDF-PVP) was employed for the on-field qualitative detection of Hg²⁺ and ranitidine. The mechanistic insights into the sensing were well explored with the help of different modern analytical techniques. The ground-state complexation and inner filter effect were responsible for fluorescence quenching in the presence of Hg²⁺ and ranitidine, respectively. Furthermore, the catalytic performance of 1′ was investigated in the Friedel–Crafts alkylation reaction between indole and β-nitrostyrene in toluene at 70 °C and the product was observed in 98% yield. The solid maintained its activity up to four cycles. The integrity and morphology of the four times used 1′ are identical to those of pristine 1′. The catalyst was also active to prepare a series of products under the optimized conditions.