Phosphinic acid functionalized carbon nanotubes for sensitive and selective sensing of chromium(VI)

•SWCNTs have been conjugated with bis(2,4,4-trimethylpentyl) phosphinic acid (PA/d).•SWCNT-PA/d adduct is demonstrated for electrochemical sensing of Cr(VI).•Linear response is obtained for 0.01–10ppb Cr(VI).•Sensitivity and the limit of detection are 35±4nA/ppb and 0.01ppb, respectively.•Proposed sensing of Cr(VI) is selective with respect to many other metals. Single-walled carbon nanotubes (SWCNTs) have been functionalized with a phosphinic acid derivative ‘bis(2,4,4-trimethylpentyl) phosphinic acid’ (PA/d). It has been achieved by treating the chlorinated SWCNTs with PA/d at 80°C. Successful functionalization and different nanomaterial properties have been investigated by UV–vis–NIR, FTIR, Raman spectroscopy, AFM and FE-SEM. PA/d conjugated SWCNTs (CNT–PA) are dispersible in some common organic solvents, e.g. CH2Cl2, DMF, CHCl3, and THF. The ‘CNT–PA’ complex was spin-casted on boron doped silicon wafer. Thus fabricated sensing electrode is demonstrated for sensitive and selective electrochemical sensing of chromium(VI) ions. A linear response is obtained over a wide range of Cr(VI) concentration (0.01–10ppb). The sensor's sensitivity and the limit of detection are observed to be 35±4nA/ppb and 0.01ppb, respectively. The practical utility of the proposed sensor is demonstrated by determining the Cr(VI) concentration in an industrial effluent sample and an underground water sample.