Electrochemical surface reconstruction of Prussian blue-modified nickel sulfide to form iron-nickel bilayer hydroxyl oxides for efficient and stable oxygen evolution reaction processes

Defect-regulated reduced graphene oxide anchored Prussian blue and platinum nanoparticles peroxidase for electrochemical detection of mesenchymal circulating tumor cells

The precise analysis of mesenchymal circulating tumor cells (mCTCs), known for their enhanced migratory behavior in peripheral blood, is essential for cancer diagnosis and predicting metastasis. Nevertheless, the rarity and heterogeneity of mCTCs present significant challenges in both their capture and subsequent enumeration. Therefore, designing and realizing a high-performance and adaptable cytosensor platform are crucial for the accurate analyzing various mCTCs. Defect engineering is used to enhance the synthesis of a peroxidase mimic enzyme, achieving significantly higher activity than natural enzymes. This was accomplished by anchoring Prussian blue (PB) and platinum (Pt) nanoparticles onto reduced graphene oxide (rGO), forming rGO@PB/Pt. An electrochemical cytosensor was subsequently constructed based on rGO@PB/Pt linked with aptamers to capture mCTCs and degrade the trace hydrogen peroxide (H2O2) secreted by mCTCs. Specifically, the presence of Fe2+ vacancies creates numerous active Fe3+ sites, resulting in an enlarged specific surface area and a microporous structure with pore diameters of approximately 0.8 nm and 1.3 nm. These structural features enable the effective encapsulation of H2O2, enhancing its rate of decomposition. The cytosensor demonstrated a linear response within the range of 1 to 104 cells/mL, with a detection limit (LOD) as low as 0.1 cells/mL (S/N = 3). Moreover, the cytosensor can quantify mCTCs solely based on cell membrane epitopes, making it applicable to almost all types of CTCs by altering the capture aptamer. In addition, the analysis of mCTCs in human blood additionally validates it as a promising candidate for the precise detection of mCTCs in clinical settings.

Ultrafine Ni-Doped FeOOH Nanoparticles with Rich Oxygen Vacancies to Promote Oxygen Evolution

Nickel iron hydroxide oxide is one of the efficient catalysts for oxygen evolution reaction (OER). However, current synthesis methods, such as solvothermal and electrodeposition, require stringent experimental conditions (e.g., temperature, pressure, and solvent) and involve complex procedures with high costs. To address this issue, we developed a simple and efficient electrostatic self-assembly strategy to synthesize Ni-doped iron oxyhydroxide (Ni-FeOOH) by combining aminated two-dimensional g-C3N4 with trace amounts of Ni2+ and Fe2+, forming a tightly integrated heterostructure (Ni-FeOOH@g-C3N4). This method is notable for its simplicity and ability to produce ultrasmall Ni-FeOOH nanoparticles (∼1.9 nm), which significantly enhance the active surface area and functional sites. The resulting catalyst exhibits exceptional OER performance, achieving a low overpotential of 260 mV at 10 mA·cm-2 and demonstrating long-term stability. Remarkably, despite containing only trace amounts of Ni (2.46%) and Fe (3.36%), Ni-FeOOH@g-C3N4 delivers a high turnover frequency of 3.96 s-1, outperforming many conventional hydroxyl oxides. The improved performance is attributed to the ultrasmall particle size and the presence of excessive oxygen vacancies, which lower the energy barrier for O* formation and accelerate OER kinetics. This work proposes a method for constructing efficient catalysts with trace active metals to improve the OER activity.

Ferrocene-MOFs: Optimizing OER Kinetics for Water Splitting

Optimizing the adsorption and desorption kinetics of oxygen evolution reaction (OER) is crucial for efficient overall water splitting. Herein, we report a series of porous ferrocene-based metal-organic framework (MFc-MOF, M = Co, Ni, Fe, Mn) nanoflowers featuring a close π-π stacking lattice structure as model catalysts, and explore the structure-activity relationship. Operando electrochemical impedance spectroscopy implies that the synthesized CoFc-MOF@NF facilitates intermediate adsorption and desorption. It exhibits an ultralow overpotential of 189 mV at 10 mA cm-2 and maintains stability for 250 h. In an overall water splitting device, when CoFc-MOF@NF serves as the anode, it yields a significantly lower cell voltage than commercial RuO2 and shows excellent stability at 100 mA cm-2 for 100 h. In situ Raman spectroscopy reveals that the CoFc-MOF@NF surface transforms into CoFeOOH, the OER-active species, while preserving the MOF framework. The inner MOF's ferrocene units act as efficient electron-transfer mediators. These findings highlight CoFc-MOF@NF's potential as a leading catalyst for sustainable water splitting hydrogen production, combining high catalytic activity, rapid kinetics, and robust stability. This work presents a new approach to balance activity and stability in MOF-based OER catalysts.

Electrochemical reconfiguration of iron-modified Ni3S2 surface induced oxygen vacancies to immobilize sulfate for enhanced oxygen evolution reaction

There is an urgent need for highly active, durable, and low-cost electrocatalysts to overcome the shortcomings of high overpotential in the oxygen evolution reaction (OER) process. In this work, the nickel-iron hydroxysulfate rich in sulfate and oxygen vacancies (SO42-@Fe-NiOOH-Ov/NiS) is legitimately constructed. SO42-@Fe-NiOOH-Ov/NiS only requires a low overpotentials of 190 mV and 232 mV at 10 mA cm-2 and 100 mA cm-2 current densities in 1 M KOH, with excellent stability for 200 h at 100 mA cm-2 current density. In situ Raman spectroscopy and Fourier transform infrared spectroscopy demonstrated the stable adsorption of more SO42- on the surface of catalyst. Density functional theory calculations testify surface reconstruction, doped Fe and oxygen vacancies significantly reduced the adsorption energy of sulfate on the surface. More importantly, the formation of *OOH to O2 is facilitated by the highly hydrogen bonding between SO42- and *OOH, accelerating the OER process.

Surface reconstruction of pyrite-type transition metal sulfides during oxygen evolution reaction

Reconstruction universally occurs over non-layered transition metal sulfides (TMSs) during oxygen evolution reaction (OER), leading to the formation of active species metal (oxy)hydroxide and thus significantly influences the OER performance. However, the reconstruction process and underlying mechanism quantitatively remain largely unexplored. Herein, we proposed an electrochemical reaction mechanism, namely sulfide oxidation reaction (SOR), to elucidate the reconstruction process of pyrite-type TMSs. Based on this mechanism, we evaluated the reconstruction capability of NiS2 doped with transition metals V, Cr, Mn, Fe, Co, Cu, Mo, Ru, Rh, and Ir within different doped systems. Two key descriptors were thus proposed to describe the reconstruction abilities of TMSs: USOR (the theoretical electric potential of SOR) and ΔU (the difference between the theoretical electric potential of SOR and OER), representing the initiation electric potential of reconstruction and the intrinsic reconstruction abilities of TMSs, respectively. Our finding shows that a lower USOR readily initiate reconstruction at a lower potential and a larger ΔU indicating a poorer reconstruction ability of the catalyst during OER. Furthermore, Fe-doped CoS2 was used to validate the rationality of our proposed descriptors, being consistent with the experiment findings. Our work provides a new perspective on understanding the reconstruction mechanism and quantifying the reconstruction of TMSs.

Agro-Waste Valorization into Carbonaceous Eco-Hydrogel: A Circular Economy and Zero Waste Tactic for Doxorubicin Removal in Water/Wastewater

The existing work aims to evaluate the efficiency of eco-hydrogel for adsorption of pollutants prepared from biopolymeric matrix and agricultural waste-derived biochar. An efficient and reusable adsorbent, designed from the integration of maize stalk activated carbon into a gelatin-alginate composite (MSAC@GE-SA) was explored for removal of doxorubicin hydrochloride (Doxo.HCL) from polluted water. The structural properties, presence of surface functional groups, and elemental composition were explored using XRD, SEM, BET, FTIR, and XPS techniques. The key adsorption parameters such as Doxo.HCL concentration, MSAC@GE-SA amount, solution pH, and the contact time between adsorbate and adsorbents were successfully optimized for the effective removal of Doxo.HCL (qmax = 239.41 mg g-1). The kinetic mechanism of MSAC@GE-SA fits well with a pseudo-second-order rate model (R2 = 0.980), followed by mono- and multilayered Langmuir and Freundlich isotherms with R2 values 0.991 and 0.993, respectively. The recyclability of MSAC@GE-SA showed great stability without any physical damage and having sustained removal efficiency up to 10 cycles (96.32 to 55.66%). The versatility of MSAC@GE-SA was further investigated for river, canal, and sewage water samples under identical experimental conditions. The practicality of the MSAC@GE-SA was evaluated by spiking Doxo.HCL into industrial effluents via the standard addition method. Subsequently, the chemical oxygen demand (COD) of the treated pollutants exhibited a notable reduction, decreasing significantly from 128 to 80 mg L-1. Following 10 successful adsorption-desorption cycles, the spent MSAC@GE-SA was utilized as a fertilizer for Vigna radiata plants, positively contributing to overall plant growth without causing harm. Hence, proposed adsorbent (MSAC@GE-SA) emerges as a viable and sustainable solution, demonstrating features of reusability and cost-effectiveness. It holds significant promise for the removal of pharmaceutical pollutants, aligning with the principles of circular economy and zero-waste tactics.