Electrochemical Performance of Reduced Graphene Oxide (rGO) Decorated Lanthanum Oxide (La2O3) Composite Nanostructure as Asymmetric Supercapacitors

Construction of p-n-p nano heterojunction through coupling La2O3, (BiO)2CO3 and Ag3PO4 for effective photocatalytic degradation of doxycycline: Insights into mechanism, pathway and intermediate toxicity evaluation

The present work is centred around the development of La2O3/(BiO)2CO3/Ag3PO4 (LBA), a p-n-p nano-heterojunction to photodegrade doxycycline under visible light irradiation. Here, ultrasonication assisted co-precipitation method was employed to synthesize the photocatalyst. The photocatalyst was characterized using different analysis such as SEM, TEM, elemental mapping, XRD, XPS, FTIR, Raman, BET, DRS, PL and EIS which confirmed the successful fabrication of LBA and their excellent ability to refrain the e-/h+ recombination owing to the construction of the heterojunction. LBA was found to degrade DOX by 91.75 % with the high mineralization of 87.23%. The impact of the reaction parameters influencing the photodegradation process including the concentration of the NCs and DOX, pH and the influence of the commonly present anions were studied. The stability and reusability of the LBA was assessed through subjecting it to four cycles of photodegradation of DOX. In addition, the recovered LBA was characterized through XPS and XRD analysis to confirm the particles stability and reusability. The active participation of the photogenerated charges and the reactive oxygen species were identified through the scavenging assay and ESR analysis. Further, GC-MS/MS analysis was performed to put forward a plausible photodegradation pathway. The toxicity of the end products as well as the intermediates was predicted through ECOSAR software.

Preconcentration of phosphate ions on graphene oxide decorated with lanthanum oxide from waters followed by energy dispersive X-ray fluorescence spectrometric determination

A method for energy dispersive X-ray fluorescence spectrometric (EDXRF) determination of phosphate ions via the PKα line in diverse types of water samples is described. The method is based on ultrasonically assisted dispersive micro-solid phase extraction (USA-DMSPE) using lanthanum oxide supported on graphene oxide (La2O3-GO) as a solid adsorbent. Under optimal preconcentration conditions, i.e. sample pH = 5, sample volume 50 mL, adsorbent dose 0.8 mg, sonication time 30 min, a linear response was obtained between the phosphate concentration and the measured analytical signal in the range of 2-300 ng mL-1 with a correlation coefficient of 0.9995. The developed procedure is characterized by good detection and quantification limits of 0.4 and 1.32 ng mL-1. The inter-day and infra-day precision of the method tested at analyte ion concentrations of 5, 50, and 200 ng mL-1 ranges from 1.1 to 4.4% and 1.2-4.7%, respectively. The accuracy of the method was verified by the standard addition method and the inductively coupled plasma atomic emission spectrometry (ICP-OES) comparative technique. The method was implemented for the analysis of various water samples, including artificial seawater. The phosphate content in studied water samples ranges from 23.8 to 121 ng mL-1. Recoveries in samples enriched with phosphates with a known concentration of 94-102%, as well as a relative difference of 1.5-3.8% between results obtained by USA-DMSPE/EDXRF and ICP-OES indicate the usefulness of the method for the quantitative determination of phosphate ions in natural waters. Moreover, the mechanism of chemisorption in the tested system was discussed and the maximum adsorption capacity of La2O3-GO towards phosphate ions (90.1 mg g-1) was determined.

Composition and Electronic Structure of La2O3/CNFs@C Core-Shell Nanoparticles with Variable Oxygen Content

La2O3 nanoparticles stabilized on carbon nanoflake (CNF) matrix were synthesized and graphitized to produce core-shell structures La2O3/CNFs@C. Further oxidation of these structures by nitric acid vapors for 1, 3 or 6 h was performed, and surface-oxidized particles La2O3/CNFs@C_x (x = 1, 3, 6) were produced. Bulk and surface compositions of La2O3/CNFs@C and La2O3/CNFs@C_x were investigated by thermogravimetric analysis and X-ray photoelectron spectroscopy. With increasing the duration of oxidation, the oxygen and La2O3 content in the La2O3/CNFs@C_x samples increased. The electronic structures of samples were assessed by electron paramagnetic resonance. Two paramagnetic centers were associated with unpaired localized and mobile electrons and were registered in all samples. The correlation between bulk and surface compositions of the samples and their electronic structures was investigated for the first time. The impact of the ratio between sp2- and sp3-hybridized C atoms, the number and nature of oxygen-containing groups on the surface and the presence and proportion of coordinated La atoms on the EPR spectra was demonstrated.

A La2O3/MXene composite electrode for supercapacitors with improved capacitance and cycling performance

Developing efficient electrode materials is a key towards high power electrochemical energy storage devices. Two-dimensional (2D) MXene shows excellent conductivity and electrochemical performance among other materials. However, the restacking of MXene layers may degrade their specific capacity and cycling performance. Considering this challenge, here we have designed a composite made of 2D MXene nanosheets and lanthanum oxide (La2O3) nanoparticles to overcome the limitations. The bifunctionality of La2O3 nanoparticles prevents the restacking of MXene layers and enhances the electrochemical properties of the electrode due to its good Faradic characteristics. The specific capacitance of the La2O3/MXene composite electrode is 366 F/g at 1 A/g, which is 4.5 and 3 times higher than those of the individual La2O3 and MXene. The composite electrode displays a capacitance retention of 96% after 1,000 cycles, which is due to synergistic effects between the two components and indicates the potential of La2O3/MXene composite for supercapacitors.

Highly selective CO2 sensing response of lanthanum oxide nanoparticle electrodes at ambient temperature

Lanthanum oxide nanoparticles (La₂O₃ NPs) are attractive rare earth metal oxides because of their applications in optical devices, catalysts, dielectric layers, and sensors. Herein, we report room temperature operative carbon dioxide gas sensing electrodes developed by a simple sonication assisted hydrothermal method. The physiochemical, morphological and gas-sensing properties of the prepared nanoparticles were studied systematically and their successful preparation was confirmed with the absence of impurities and high selectivity towards CO₂. The fabricated sensor showed a high sensitivity of 40% towards CO₂ at 50 ppm, and it can detect concentrations of up to 5 ppm with a quick response time of 6 s and recovery of 5 s. The electrode demonstrated long-term stability of 95% for 50 days when tested with an interval of 10 days. This simple and cost-effective method shows great potential for fabricating room temperature CO₂ gas sensors.