Molecular modeling analyses for graphene functionalized with Fe3O4 and NiO

Potential of carbon micro/nanofibers derived from lignocellulose biomass valorisation for CO2 adsorption: A review on decarbonization biotechnology for climate change solutions

Biomass, as a source of lignocellulose, can be valorized into carbon micro/nanofibers for adsorbing greenhouse gas (GHGs) emissions, especially CO2. This article is derived from systematic evidence evaluation of published studies, presenting new, innovative, and systemic approaches to lignocellulose-based carbon micro/nanofiber studies. The review covers a general overview of carbon micro/nanofiber studies, mapping chronicles of the studies, carbon micro/nanofiber types for CO2 uptake, carbon micro/nanofibers fabrication and characterization, obtained carbonaceous material activation and performances, regulatory frameworks, and sustainability. The published studies show that carbon fiber has been researched for GHG emissions adsorption since the 1950s, with an increasing trend of publication numbers. The trend of studies has commenced from activated carbon to nanocarbonaceous materials and their composites. The excellent performance of both micro/nano-sized carbon provides promising opportunities for absorbing CO2 and other GHGs, such as NO2 and CH4, facilitating decarbonization. Several types of carbonaceous activation processes and modifications were utilized to enhance the performances of the resultant biochars, especially in surface materials, CO2 adsorption capacity, and CO2 selectivity. Proposed mechanisms for the absorption of CO2 by activated carbonaceous materials through physisorption and chemisorption were also observed. To date, regulatory frameworks on the use of activated carbon for CO2 capture are still rarely found, but biochar has been mainstreamed and regulated internationally for CO2 removal. Other regulations have been enacted but have not yet internationally harmonized, mostly focusing on the terminology of carbon nanotubes, characterization, general applications, labelling, packaging, transportation, and the effects of toxicity on health. This study also proposed the sustainability aspects and performance indicators that can be used for circular economy application with an ultimate goal of climate change mitigation through GHG reduction. Besides the regulatory framework, elements of the business model and sustainability were proposed in the circular economy framework of the fibers. By scoping carbon micro/nanofibers studies, it is shown with obvious evidence that carbon micro/nanofibers and their composites have the potential for CO2 adsorption and removal, leading to the acceleration of the decarbonization process that is in line with the Paris Agreement, especially in applying innovative CO2 capture, storage, and utilization (CCSU) technologies.

Effects of Graphene Oxide (GO) and Reduced Graphene Oxide (rGO) on Green-Emitting Conjugated Copolymer's Optical and Laser Properties Using Simulation and Experimental Studies

The properties of a conjugated copolymer (CP), poly[(9,9-Dioctyl-2,7-divinylenefluorenylene)-alt-co-(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene) (PDVF-co-MEH-PV), were investigated in the presence of graphene oxide (GO) and reduced graphene oxide (rGO) using absorption, fluorescence, laser, and time-resolved spectroscopy. CPs are usually dissolved in low-polar solvents. Although GO does not dissolve well, rGO and PDVF-co-MEH-PV dissolve in chloroform due to their oxygen acceptor sites. Hence, we studied rGO/PDVF-co-MEH-PV (CP/rGO), performing all experiments and simulations in chloroform. We performed simulations on PDVF-co-MEH-PV, approximate GO, and rGO using time-dependent density-functional theory calculations to comprehend the molecular dynamics and interactions at the molecular level. The simulation polymer used a tail-truncated oligomer model with up to three monomer units. The simulation and experimental results were in agreement. Further, the PDVF-co-MEH-PV exhibited fluorescence, laser quenching, rGO-mediated laser blinking, and spectral broadening effects when GO and rGO concentrations increased. The experimental and simulation results were compared to provide a plausible mechanism of interaction between PDVF-co-MEH-PV and rGO. We observed that for lower concentrations of rGO, the interaction did not considerably decrease the amplified spontaneous emissions of PDVF-co-MEH-PV. However, the fluorescence of PDVF-co-MEH-PV was considerably quenched at higher concentrations of rGO. These results could be helpful for future applications, such as in sensors, solar cells, and optoelectronic device design. To demonstrate the sensor capability of these composites, a paper-based sensor was designed to detect ethanol and nitrotoluene. An instrumentation setup was proposed that is cheap, reusable, and multifunctional.

Distinct chromium removal mechanisms by iron-modified biochar under varying pH: Role of iron and chromium speciation

Iron-modified biochar (Fe-biochar) has been widely developed to attenuate Cr(VI) pollution in both acid and alkaline environments. However, there are few comprehensive studies on how the iron speciation in Fe-biochar and chromium speciation in solution influencing the removal of Cr(VI) and Cr(III) under varying pH. Here, multiple Fe-biochar containing Fe3O4 or Fe(0) were prepared and applied to remove aqueous Cr(VI). Kinetics and isotherms suggested that all Fe-biochar could efficiently remove Cr(VI) and Cr(III) via adsorption-reduction-adsorption. The Fe3O4-biochar immobilized Cr(III) by forming FeCr2O4, while amorphous Fe-Cr coprecipitate and Cr(OH)3 was formed when using Fe(0)-biochar. Density functional theory (DFT) analysis further indicated that pH increase caused more negative adsorption energies between Fe(0)-biochar and the pH-dependent Cr(VI)/Cr(III) species. Consequently, the adsorption and immobilization of Cr(VI) and Cr(III) species by Fe(0)-biochar was more favored at higher pH. In comparison, Fe3O4-biochar exhibited weaker adsorption abilities for Cr(VI) and Cr(III), which were in consistent with their less negative adsorption energies. Nonetheless, Fe(0)-biochar merely reduced ∼70% of adsorbed Cr(VI), while ∼90% of adsorbed Cr(VI) was reduced by Fe3O4-biochar. These results unveiled the importance of iron and chromium speciation for chromium removal under varying pH, and might guide the application-oriented design of multifunctional Fe-biochar for broad environmental remediation.

Functionalized Graphene Oxide with Chitosan for Dopamine Biosensing

Detecting biological structures via a rapid and facile method has become a pronounced point of research. Dopamine (DA) detection is critical for the early diagnosis of a variety of neurological diseases/disorders. A study on the real-time optical detection of DA is described here using graphene oxide (GO) functionalized with chitosan (Cs). Hence, a computational model dependent on a high theoretical level density functional theory (DFT) using the B3LYP/LANL2DZ model is carried out to study the physical as well as electronic properties of the proposed interaction between GO functionalized with Cs and its interaction with DA. GO functionalized with a Cs biopolymer was verified as having much higher stability and reactivity. Moreover, the addition of DA to functionalized GO yields structures with the same stability and reactivity. This ensures that GO-Cs is a stable structure with a strong interaction with DA, which is energetically preferred. Molecular electrostatic potential (MESP) calculation maps indicated that the impact of an interaction between GO and Cs increases the number of electron clouds at the terminals, ensuring the great ability of this composite when interacting with DA. Hence, these calculations and experimental results support the feasibility of using GO functionalized with Cs as a DA biosensor.

Exploring Molecular and Electronic Property Predictions of Reduced Graphene Oxide Nanoflakes via Density Functional Theory

In this research, we perform a theoretical interpretation of molecular and electronic properties of reduced graphene oxide (rGO) nanoflakes through the density functional theory. Here, two pristine graphene nanoflake systems were passivated by hydrogen atoms at their edges, armchair (C58H20) and zigzag (C54H20); besides, we implemented 12 rGO systems with a range of low oxide coverage (1, 3, and 4%). Computational calculations were carried out employing the functional hybrid B3LYP and the basis 6-31G(d, p) and 6-311G(d, p) levels of theory. We brought the proposed molecular structures to a stable minimum. We determined the global reactivity descriptors through chemical potential, hardness, softness, and index of electrophilicity. Besides, the maps of electrostatic potential were generated. We found that the hydroxyl and epoxy functional groups dope the graphene molecule in p-type and n-type forms, respectively. In addition, we could attribute the increases of the oxide coverage and the chemical potential to the softness of the molecule. These results suggest that structures with this type of doping can help in developing advanced electronics of sensors and devices.

Graphene/Fe3O4 Nanocomposite as a Promising Material for Chemical Current Sources: A Theoretical Study

The outstanding mechanical and conductive properties of graphene and high theoretical capacity of magnetite make a composite based on these two structures a prospective material for application in flexible energy storage devices. In this study using quantum chemical methods, the influence of magnetite concentration on energetic and electronic parameters of graphene/Fe₃O₄ composites is estimated. It is found that the addition of magnetite to pure graphene significantly changes its zone structure and capacitive properties. By varying the concentration of Fe₃O₄ particles, it is possible to tune the capacity of the composite for application in hybrid and symmetric supercapacitors.

Modified Ziziphus spina-christi stones as green route for the removal of heavy metals

Green routes for remediation of heavy metals are worldwide challenges to overcome pollution problems on one hand and control the adverse impact of chemicals on the other hand. Biosorption is one of the most effective methods for removing lower level of heavy metals. The idea to apply natural resources as a green method for removal of heavy metals, this route has no adverse impacts on the environment. This study investigated the ability of chemically modified Ziziphus spina-christi stones (ZSCs) as agriculture by-products to perform the biosorption of Pb(II), Zn(II) and Cd(II) ions from wastewater in a single and ternary metal system. The characteristic functional groups of chemically modified ZSCs were analyzed by Fourier transform infrared. In comparison with acidic ZSCs, alkali-modified ZSCs by KOH was more effective and enhanced the removal efficiency of ZSCs. Using Langmuir isotherm, the maximum adsorption capacity on the modified ZSCs for Pb(II) was 9.06 mg/g, for Zn(II) obtained by using ZSC-citric acid was 4.19 mg/g and 5.38 mg/g for Cd(II) as obtained by using ZSC-H2O2. The molecular electrostatic potential, which was calculated at B3LYP/6-31G(d,p), indicated that each metal is di-hydrated, forming a complex with two units of amino acids. This mechanism demonstrated the uptake process by ZSCs.