Phosphomolybdates for Dual-Mode Photoelectrochemical Sensing toward Trace Chromium(VI) and Tetracycline.

Highly sensitive photoelectrochemical (PEC) sensors for trace carcinogens, such as heavy metal chromium(VI) [Cr(VI)] and antibiotic tetracycline (TC) are crucial. Herein, by integration of photoactive and redox phosphomolybdates with conjugated organic components, types of dual-mode PEC sensors were synthesized for sensing trace Cr(VI) and TC pollutants, with formulas of (H 2 bimb) 2 [Co 2 (bimb) 1.5 ][Co(H 2 O) 4 ][Co(P 4 Mo 6 O 31 H 6 ) 2 ]·6H 2 O ( 1 ), (H 2 bib) 2 [Co(H 2 O) 3 ][Co 2 (H 2 O) 5 ][Co(P 4 Mo 6 O 31 H 6 ) 2 ]·9H 2 O ( 2 ), and (H 2 bib) 6 [Co(Hbib) 2 (H 2 O) 5 ][Co(P 4 Mo 6 O 31 H 7 ) 2 ] 2 ·15H 2 O ( 3 ), where bimb represents 1,4-bis(1-imidazolyl)benzene and bib is 4,4'-bis(imidazolyl)bibphenyl. Hybrid 1 consisted of a three-dimensional framework structure constructed by Co{P 4 Mo 6 } 2 clusters and one-dimensional (1D) {Co-bimb} chains, hybrid 2 exhibited 1D Co ion-bridged Co{P 4 Mo 6 } 2 chains hydrogen-bonding with [H 2 bib] 2+ cations, and hybrid 3 showed a discrete hybrid structure built upon a Co{P 4 Mo 6 } 2 cluster modified by the {Co-bib} unit. Hybrids 1 - 3 displayed wide spectral absorption and excellent electrochemical redox properties, enabling dual-mode PEC responses to Cr(VI) reduction and TC oxidation. For Cr(VI) detection, hybrids 1 - 3 exhibited high sensitivities of 364.40, 225.72, and 124.29 μA·μM -1 as well as "nM" level detection limits (LODs) of 4.9, 10.0, and 11.0 nM, respectively. For TC detection, the sensitivities of hybrids 1 - 3 were 494.72, 308.78, and 174.03 μA·μM -1 and the LODs were 5.2, 6.1, and 12.9 nM, respectively. This research offers significant insights into designing efficient PEC sensors for the detection of environmental pollutants.