Large magnetocaloric effect and critical behavior in Sm

The magnetic properties and magnetocaloric effect (MCE) in electron-doped Sm0.09Ca0.91MnO3 nanomanganite have been investigated in detail by magnetization and heat capacity measurements. The maximum magnetic entropy change $(|\Delta S_{\text{M}}|)$ and the relative cooling power (RCP) are found to be, respectively, $8.59\ \text{Jkg}^{-1}\text{K}^{-1}$ and $1522\ \text{mJ/cm}^{3}$ for a 7 T magnetic field change along with a negligible hysteresis loss, making of this material a promising candidate for magnetic refrigeration at low temperature. The maximum value of $|\Delta S_{\text{M}}|$ occurs close to the Curie temperature $(T_{\text{C}})$ . The values of $|\Delta S_{\text{M}}|$ and RCP are comparable to a few hole-doped manganite. To investigate the nature of the paramagnetic-to-ferromagnetic phase transition, critical exponent study has been carried out. Based on the modified Arrott plot, we have determined the values of critical parameters ($T_{\text{C}},\beta,\gamma$ and δ) and conclusively shown that Sm0.09Ca0.91MnO3 has nearly mean-field–like long-range interaction. The calculated values of critical exponents not only obey the scaling hypothesis, but also corroborate the results obtained employing the Kouvel-Fisher method. The re-scaled magnetic entropy change curves for different applied magnetic fields collapse into a single master curve for this electron-doped manganite indicating clearly a second-order magnetic phase transition. Such noticeably large $|\Delta S_{\text{M}}|$ at low magnetic field makes this material a potential candidate for low-temperature magnetic refrigeration

Biomimetic Approach toward Visible Light-Driven Hydrogen Generation Based on a Porphyrin-Based Coordination Polymer Gel

There has been a widespread interest in developing self-assembled porphyrin nanostructures to mimic nature’s light-harvesting processes. Herein, porphyrin-based coordination polymer gel (CPG) has been developed as a “soft” photocatalyst material for hydrogen (H2) production from water under visible light. The CPG offers a hierarchical nanofibrous network structure obtained through self-assembly of a terpyridine alkyl-amide appended porphyrin (TPY-POR)-based low molecular weight gelator with ruthenium ions (RuII) and produces H2 with a rate of 5.7 mmol g–1 h–1 in the presence of triethylamine (TEA) as a sacrificial electron donor. Further, the [Fe2(bdt)(CO)6] (dbt = 1,2-benzenedithiol) cocatalyst, which can mimic the activity of iron hydrogenase, is coassembled in the CPG and shows remarkable improvement in H2 evolution (catalytic activity; rate ∼10.6 mmol g–1 h–1 and turnover number ∼1287). The significant enhancement in catalytic activity was supported by several controlled experiments, including femtosecond transient absorption (TA) spectroscopy and also DFT calculation. The TA study supported the cascade electron transfer process from porphyrin core to [Ru(TPY)2]2+ center, and subsequently, the electron transfers to the cocatalyst [Fe2(bdt)(CO)6] for H2 production