B@LGTs of Nd, Eu, Er, and Yb lanthanides with physicochemical interfacing for enhanced photocatalytic reduction of fluorescent dyes, transition metal ions, and quinonoid phenolphthalein†

In this work, lanthanide sulphide nanorods (LSNRs) of neodymium (Nd₂S₃), europium (Eu₂S₃), erbium (Er₂S₃), and ytterbium (Yb₂S₃) were prepared with a LnCl₃·6H₂O salt, sodium metal, and H₂S gas through a crash reaction methodology (CRM) at NTP. The LSNRs were doped with gadolinium ions (Gd³⁺) and coated with graphene oxide (GO) to prepare bimetallic LSNRs (B@LSNRs) and GO templates (B@LGTs), respectively. LSNRs, B@LSNRs, and B@LGTs were characterised using XRD, FT-IR spectroscopy, BET analysis, UV/vis spectroscopy, HR-TEM, SEM, TGA/DTG, XPS, Raman spectroscopy, and elemental analysis. The B@LGTs as interstitial photocatalysts photocatalytically reduced the Coomassie brilliant blue red (BBR) dye, transition metal ions (TMIs), and quinonoid phenolphthalein (QHIn) in aqueous solutions under visible light. Experimental parameters including pollutant concentrations, B@LGT dosages, physicochemical properties (PCPs), and pH were optimized for achieving monodispersion and maximum PCR. The PCPs like density, viscosity, sound velocity, surface tension, friccohesity, and isentropic compressibility have predicted the spontaneity and sustainability at 288.15, 298.15, and 310.15 K with photocatalysing medium. B@Nd₂S₃:GO, B@Eu₂S₃:GO, B@Er₂S₃:GO, and B@Yb₂S₃:GO with 2.23, 2.28, 2.38, and 1.88 eV bandgaps (E_g) and −670.14, −829.18, −767.39, and −925.57 J mol⁻¹ activation energies (E_a) having −0.9869, 0.8843, −1.4011, and −1.2102 J mol⁻¹ entropies (ΔS) photocatalytically reduced a dye with 96.35, 96.67, 97.60, and 99.17% quantum yields (Φ), respectively. The above-mentioned data indicated that the B@LGTs are robust photocatalysts that photocatalytically reduce BBR in 48 and 30 times shorter duration than LSNRs and B@LSNRs, respectively. It was found that 0.01 g% B@LGTs photocatalytically reduced 40 ppm BBR and 20 ppm CrCl₃, NiCl₂, CuCl₂, and QHIn in 30, 20, 40, 35, and 15 min, respectively. Kinetic rate constants of 3.25 × 10⁻², 3.21 × 10⁻², 3.18 × 10⁻² and 3.15 × 10⁻² min⁻¹ for BBR were in the order of B@Nd₂S₃:GO > B@Er₂S₃:GO > B@Eu₂S₃:GO > B@Yb₂S₃:GO with 4f^3e, 4f^11e, 4f^6e, and 4f^13e electrons, respectively. This indicated first-order reaction similar to QHIn and TMIs. Furthermore, the B@LGTs exhibited favourable stabilities, with 58.1–68.05% PCR efficiencies after 10 cycles of reduction experiments.