Surface Anions Research Articles

Hierarchical assembly of Ag40 nanowheel ranging from building blocks to diverse superstructure regulation

Achieving precise and controllable hierarchical self-assembly of functional nanoclusters within crystal lattices to create distinct architectures is of immense significance, yet it creates considerable challenges. Here we successfully synthesized a silver nanowheel Ag40, along with its optically pure enantiomers S-/R-Ag40. Each species possesses an internal nanospace and exhibits host-guest interactions. These structures are constructed from primary building blocks (Ag9). By manipulating the surface anions and guest molecules, the nanowheels function as secondary building blocks, spontaneously organizing into complex double- and triple-helical crystalline superstructures or one-dimensional chains {Ag41}n through conformational matching and diverse noncovalent interactions. Moreover, we demonstrate that the water-mediated complex specifically assembled with uridine monophosphate nucleotides, resulting in chiral assemblies of Ag40 that exhibit chiroptical activity for specific recognition. Our findings provide insights into the efficient construction of assemblies with hollow frameworks and propose strategies for superstructure engineering by manipulating surface motifs.

Effect of Surface Anions Adsorbed by Rutile TiO2 (001) on Photocatalytic Nitrogen Reduction Reaction: A Density Functional Theory Calculation

The adsorption of common anions found in water can have a considerable impact on the surface state and optical characteristics of titanium dioxide (TiO2), which has an important impact on the photocatalytic nitrogen reduction reaction (NRR). This work utilizes density functional theory (DFT) computations to examine the electronic and optical characteristics of the TiO2 (001) surface under various anion adsorptions in order to clarify their influence on the photocatalytic NRR of TiO2. The modifications in the structure, optical, and electronic properties of TiO2 before and after anion adsorption are investigated. In addition, the routes of Gibbs free energy for the NRR are also evaluated. The results indicate that the adsorption of anions modifies the surface characteristics of TiO2 to a certain degree, hence impacting the separating and recombining charge carriers by affecting the energy gap of TiO2. More importantly, the adsorption of anions can increase the energy barriers for the NRR, thereby exerting a detrimental effect on its photocatalytic activity. These findings provide a valuable theoretical contribution to understanding the photocatalytic reaction process of TiO2 and its potential application of NRR in the actual complex water phase.

Finding Natural, Dense, and Stable Frustrated Lewis Pairs on Wurtzite Crystal Surfaces for Small‐Molecule Activation

AbstractThe surface frustrated Lewis pairs (SFLPs) open up new opportunities for substituting noble metals in the activation and conversion of stable molecules. However, the applications of SFLPs on a larger scale are impeded by the complex construction process, low surface density, and sensitivity to the reaction environment. Herein, wurtzite‐structured crystals such as GaN, ZnO, and AlP are found for developing natural, dense, and stable SFLPs. It is revealed that the SFLPs can naturally exist on the (100) and (110) surfaces of wurtzite‐structured crystals. All the surface cations and anions serve as the Lewis acid and Lewis base in SFLPs, respectively, contributing to the surface density of SFLPs as high as 7.26×1014 cm−2. Ab initio molecular dynamics simulations indicate that the SFLPs can keep stable under high temperatures and the reaction atmospheres of CO and H2O. Moreover, outstanding performance for activating the given small molecules is achieved on these natural SFLPs, which originates from the optimal orbital overlap between SFLPs and small molecules. Overall, these findings not only provide a simple method to obtain dense and stable SFLPs but also unfold the nature of SFLPs toward the facile activation of small molecules.

Finding Natural, Dense, and Stable Frustrated Lewis Pairs on Wurtzite Crystal Surfaces for Small-Molecule Activation.

The surface frustrated Lewis pairs (SFLPs) open up new opportunities for substituting noble metals in the activation and conversion of stable molecules. However, the applications of SFLPs on a larger scale are impeded by the complex construction process, low surface density, and sensitivity to the reaction environment. Herein, wurtzite-structured crystals such as GaN, ZnO, and AlP are found for developing natural, dense, and stable SFLPs. It is revealed that the SFLPs can naturally exist on the (100) and (110) surfaces of wurtzite-structured crystals. All the surface cations and anions serve as the Lewis acid and Lewis base in SFLPs, respectively, contributing to the surface density of SFLPs as high as 7.26×1014 cm-2. Ab initio molecular dynamics simulations indicate that the SFLPs can keep stable under high temperatures and the reaction atmospheres of CO and H2O. Moreover, outstanding performance for activating the given small molecules is achieved on these natural SFLPs, which originates from the optimal orbital overlap between SFLPs and small molecules. Overall, these findings not only provide a simple method to obtain dense and stable SFLPs but also unfold the nature of SFLPs toward the facile activation of small molecules.

Confining bulk molecular O2 by inhibiting charge transfer on surface anions toward stable redox electrochemistry in layered oxide cathodes

Molecular O2 has been clarified as an important O-oxidation model in anionic redox, the charge compensation provided by which pushes energy-density limits of layered oxide cathodes. However, how to confine the bulk-formed molecular O2 and retard its conversation to free gaseous O2 (↑), an origin of unstable redox electrochemistry, remains open questions. Here, we propose a strategy via tuning relative values of Mott–Hubbard U and charge-transfer energy Δ to suppress charge transfer on surface anions to confine the bulk molecular O2. Supported by theoretical calculations, Nb5+ without 4d electrons which can enable U < < Δ is selected as a charge-transfer insulator. The thus Nb5+-surface-tailored model compound Na0.67Fe0.5Mn0.5O2 shows an oxygen-redox-inactive surface and well-confined bulk molecular O2 as directly uncovered by soft X-ray absorption spectroscopy and 50 K-electron paramagnetic resonance results respectively. Meanwhile, a stable redox electrochemistry with enhanced cycling stability, inhibited voltage decay and eliminated P2-O2 phase transitions is observed because of the well-caged bulk O2. More broadly, this work presents a versatile access to stabilize the important O-oxidation model, enriching approaches of stabilizing the anionic redox electrochemistry.

Surface Anion Promotes Pt Electrocatalysts with High CO Tolerance in Fuel-Cell Performance.

Platinum reaches considerable activity and stability as an electrocatalyst but is not always capable of maintaining such performance under CO poisoning, particularly in CO residual fuels for practical proton-exchange membrane fuel cells (PEMFCs). In this work, we report that surface anions including a series of nonmetal elements on Pt nanoparticles result in outstanding CO tolerance for electrocatalysts in fuel cells. In particular, phosphorus surface-anion-modified Pt (denoted as P-Pt) possesses more than 10-fold enhancement of CO tolerance (only 8.4% decay) than commercial Pt/C, which can serve as a robust electrocatalyst both in CO poisoning half cells and full cells. Moreover, the general mechanism and principle were proposed, stating that surface anions should be selected preferentially to offer electron feedback to downshift the d-band center for the Pt surface, successfully weakening CO adsorption and leading to high-tolerance capability. We anticipate that surface anions on a Pt surface can bring robust electrocatalysts for practical PEMFCs and offer novel insights for high-performance Pt-based electrocatalysts.

Enhanced thermal stability of MAPbBr3 nanocrystals by ligand modification

The intrinsic water and thermal instabilities of perovskite nanocrystals (PNCs) are considered to be a major obstacle hindering their wide potential applications in optoelectronic devices. Herein, we report the enhanced stability of MAPbBr3 (MA=methylammonium) PNCs by ligand modification of 3,3-diphenylpropylamine (DPPA) and octylamine bromide (OABr). The resultant MAPbBr3@PVDF (polyvinylidene fluoride) films could maintain 77.8% and 81.2% of original photoluminescence quantum yield (PL QY, 85.9%) once keeping at 60 ℃ and immersing in water for 7 days, respectively. The enhanced thermal stability could be mainly attributed to two situations. One is the introduced DPPA ligand, which can passivate the surface defects with large steric resistance to suppress the further growth of PNCs during heating. The other is the added OABr, which can not only coordinate to both surface cations and anions of PNCs, but also make the effective compensation of Br– vacancies stabilize the target MAPbBr3 PNCs.

Decoupling the Chemical and Mechanical Strain Effect on Steering the CO2 Activation over CeO2-Based Oxides: An Experimental and DFT Approach.

Doped ceria-based metal oxides are widely used as supports and stand-alone catalysts in reactions where CO2 is involved. Thus, it is important to understand how to tailor their CO2 adsorption behavior. In this work, steering the CO2 activation behavior of Ce–La–Cu–O ternary oxide surfaces through the combined effect of chemical and mechanical strain was thoroughly examined using both experimental and ab initio modeling approaches. Doping with aliovalent metal cations (La3+ or La3+/Cu2+) and post-synthetic ball milling were considered as the origin of the chemical and mechanical strain of CeO2, respectively. Experimentally, microwave-assisted reflux-prepared Ce–La–Cu–O ternary oxides were imposed into mechanical forces to tune the structure, redox ability, defects, and CO2 surface adsorption properties; the latter were used as key descriptors. The purpose was to decouple the combined effect of the chemical strain (εC) and mechanical strain (εM) on the modification of the Ce–La–Cu–O surface reactivity toward CO2 activation. During the ab initio calculations, the stability (energy of formation, EOvf) of different configurations of oxygen vacant sites (Ov) was assessed under biaxial tensile strain (ε > 0) and compressive strain (ε < 0), whereas the CO2-philicity of the surface was assessed at different levels of the imposed mechanical strain. The EOvf values were found to decrease with increasing tensile strain. The Ce–La–Cu–O(111) surface exhibited the lowest EOvf values for the single subsurface sites, implying that Ov may occur spontaneously upon Cu addition. The mobility of the surface and bulk oxygen anions in the lattice contributing to the Ov population was measured using 16O/18O transient isothermal isotopic exchange experiments; the maximum in the dynamic rate of 16O18O formation, Rmax(16O18O), was 13.1 and 8.5 μmol g–1 s–1 for pristine (chemically strained) and dry ball-milled (chemically and mechanically strained) oxides, respectively. The CO2 activation pathway (redox vs associative) was experimentally probed using in situ diffuse reflectance infrared Fourier transform spectroscopy. It was demonstrated that the mechanical strain increased up to 6 times the CO2 adsorption sites, though reducing their thermal stability. This result supports the mechanical actuation of the “carbonate”-bound species; the latter was in agreement with the density functional theory (DFT)-calculated C–O bond lengths and O–C–O angles. Ab initio studies shed light on the CO2 adsorption energy (Eads), suggesting a covalent bonding which is enhanced in the presence of doping and under tensile strain. Bader charge analysis probed the adsorbate/surface charge distribution and illustrated that CO2 interacts with the dual sites (acidic and basic ones) on the surface, leading to the formation of bidentate carbonate species. Density of states (DOS) studies revealed a significant Eg drop in the presence of double Ov and compressive strain, a finding with design implications in covalent type of interactions. To bridge this study with industrially important catalytic applications, Ni-supported catalysts were prepared using pristine and ball-milled oxides and evaluated for the dry reforming of methane reaction. Ball milling was found to induce modification of the metal–support interface and Ni catalyst reducibility, thus leading to an increase in the CH4 and CO2 conversions. This study opens new possibilities to manipulate the CO2 activation for a portfolio of heterogeneous reactions.

Photoinduced adsorption of Cr(VI) ions in nano‐zinc oxide and nano‐zinc oxide/polypyrrole composite

AbstractZinc oxide‐polypyrrole composites (ZnO‐PPY) are novel materials that have attracted significant attention in recent years. These materials have the potential to remove hazardous pollutants from water effectively. Here, we explore facile synthesis, characterization, and adsorption capacity of hexavalent chromium anions, by nano‐ZnO and nano‐ZnO‐PPY composite. Cold precipitation of ZnO using sodium dodecyl sulfate as an additive prevents nanoparticle growth, which permits the composite preparation with PPY. The results demonstrated that the ZnO‐PPY structure was different than ZnO, more amorphous, less porous, and with a different morphology. New Fourier transform infrared spectroscopy vibrations observed in ZnO‐PPY hinted an interaction with ZnO, leading to a more acidic surface. This information could point to the composite formation driven by interactions between oxygen groups and pyrrole nitrogen. Both materials performed better under light, indicating a photoinduced adsorption phenomenon favored by oxygen vacancies. The new composite demonstrated a reduced adsorption capacity compared to ZnO at neutral and slightly acidic pHs due to electrostatic repulsion of the negatively charged surface and Cr(VI) anions. At alkaline pHs, the pyrrolic nitrogen's is able to interact with partially charged Cr‐complex and to carry out a ligand interchange even in a not favorable charge environment. The ZnO‐PPY composite, outperformed the zinc oxide capacity.

Activated layered double hydroxides: assessing the surface anion basicity and its connection with the catalytic activity in the cyanoethylation of alcohols.

Layered double hydroxides (LDHs) act as catalysts in several reactions like in the cyanoethylation of alcohols with acrylonitrile to produce alkoxypropionitriles. Here we report an experimental and theoretical study in which it is shown that the experimental catalytic activity of LDHs in the cyanoethylation of 2-propanol and methanol correlates with the predicted strength of the basicity of the adsorbed surface species. First, it is shown that using activated LDHs containing Mg2+ and Al3+ (MgAl-LDH), Mg2+ and Ga3+ (MgGa-LDH), and Mg2+, Al3+ and Ga3+ (MgAlGa-LDH) great conversions to alkoxypropionitriles in high yields are obtained. Next, the basicity of these LDHs is estimated by means of the local softness, a local reactivity index calculated using density functional theory and appropriate surface models. For that, the adsorption of hydroxide and methoxide anions at the (001) surface of MgAl and MgGa-LDHs is investigated. We include LDHs containing Zn2+ and Al3+ (ZnAl-LDH) and Zn2+ and Ga3+ (ZnGa-LDH) in this part of the study to account for the effect of changing the divalent and trivalent metal composition on the basicity. It is found that hydroxide anions adsorbed on the MgGa-LDH surface and methoxide anions adsorbed on the MgAl-LDH surface are the most basic ones. This basicity trend correlates with our experimental findings about the catalytic activity of the activated LDHs. Further analyzing the connection between the LDH composition and the anion basicity, it is argued that the key steps dictating the LDH catalytic activity are the alcohol deprotonation in the cyanoethylation of 2-propanol, as it has been previously suggested, and the methoxide anion attack to the acrylonitrile double bond in the methanol cyanoethylation reaction.

High Loading of Transition Metal Single Atoms on Chalcogenide Catalysts.

Transition metal doped chalcogenides are one of the most important classes of catalysts that have been attracting increasing attention for petrochemical and energy related chemical transformations due to their unique physiochemical properties. For practical applications, achieving maximum atom utilization by homogeneous dispersion of metals on the surface of chalcogenides is essential. Herein, we report a detailed study of a deposition method using thiourea coordinated transition metal complexes. This method allows the preparation of a library of a wide range of single atoms including both noble and non-noble transition metals (Fe, Co, Ni, Cu, Pt, Pd, Ru) with a metal loading as high as 10 wt % on various ultrathin 2D chalcogenides (MoS2, MoSe2, WS2 and WSe2). As demonstrated by the state-of-the-art characterization, the doped single transition metal atoms interact strongly with surface anions and anion vacancies in the exfoliated 2D materials, leading to high metal dispersion in the absence of agglomeration. Taking Fe on MoS2 as a benchmark, it has been found that Fe is atomically dispersed until 10 wt %, and beyond this loading, formation of coplanar Fe clusters is evident. Atomic Fe, with a high electron density at its conduction band, exhibits a superior intrinsic activity and stability in CO2 hydrogenation to CO per Fe compared to corresponding surface Fe clusters and other Fe catalysts reported for reverse water-gas-shift reactions.

Modulation of carbon induced persulfate activation by nitrogen dopants: recent advances and perspectives

N dopants could regulate the electronic structure of carbon matrix, improve the adsorption affinity between carbon surface and PS anions, and thus pose significant effect on the carbon induced PS-AOPs.

Role of Ammonium Derivative Ligands on Optical Properties of CH3NH3PbBr3 Perovskite Nanocrystals.

Amines, ammonium salts, and their combination with organic acids are commonly employed ligands during the synthesis of colloidal perovskite nanocrystals (PNCs). However, the role of surface coordination, derived from different ammonium derivative ligands, on the optical properties of PNCs remains poorly understood. In this study, octylamine (OA), octylammonium bromide (OABr), and oleic acid (OAc) were applied, standing for amine, ammonium salt, and organic acid, respectively. The effects of four different types of ligands, including OA, OABr, OA-OAc, and OABr-OAc, on the surface coordination and subsequently optical properties of CH3NH3PbBr3 PNCs were comparatively investigated. Compared to amine ligand, the ammonium salt could coordinate to both surface cations and anions of PNCs to passivate their surface defects more effectively, leading to enhanced optical properties including higher photoluminescence (PL) spectral intensities and PL quantum yield. Moreover, the combination of OAc with amine rather than ammonium salt ligand could trigger the protonation-deprotonation reaction to further improve their coordination effect on a PNC's surface, thus leading to significantly enhanced optical properties of PNCs. This study clarified the surface coordination of different ammonium derivative ligands and their role on the optical properties of PNCs, which could guide the design of ligands during the synthesis of PNCs.

Removal of ferricyanide ions from aqueous solutions using modified red mud with cetyl trimethylammonium bromide

The reuse of red mud, an industrial waste found in alumina productions, is an efficient method to decrease the disadvantages of the industrial operation. In this study, red mud has been modified (ABC) with the surfactant of cetyl trimethylammonium bromide (CTAB) and used as a new adsorbent for the removal of ferricyanide anions from aqueous solution. The CTAB changed the charge of red mud to positive charge in a concentration above the critical micelle concentration that efficiently reduced the negative charge repulsion force between the adsorbent surface and ferricyanide anions. The equilibrium studies using two- and three-parameter models showed that the adsorption process followed the Freundlich model in which ferricyanide adsorption onto ABC was heterogeneous with a multilayer adsorption. The kinetic studies have been carried out with the consideration of pseudo-first-order, pseudo-second-order, Elovich and intraparticle diffusion models, which displayed the chemisorption interaction by intraparticle diffusion as a controlling step. Thermodynamic studies indicated that the ferricyanide adsorption process onto ABC was endothermic and spontaneous.

Finding and Fixing Traps in II-VI and III-V Colloidal Quantum Dots: The Importance of Z-Type Ligand Passivation.

Energy levels in the band gap arising from surface states can dominate the optical and electronic properties of semiconductor nanocrystal quantum dots (QDs). Recent theoretical work has predicted that such trap states in II–VI and III–V QDs arise only from two-coordinated anions on the QD surface, offering the hypothesis that Lewis acid (Z-type) ligands should be able to completely passivate these anionic trap states. In this work, we provide experimental support for this hypothesis by demonstrating that Z-type ligation is the primary cause of PL QY increase when passivating undercoordinated CdTe QDs with various metal salts. Optimized treatments with InCl3 or CdCl2 afford a near-unity (>90%) photoluminescence quantum yield (PL QY), whereas other metal halogen or carboxylate salts provide a smaller increase in PL QY as a result of weaker binding or steric repulsion. The addition of non-Lewis acidic ligands (amines, alkylammonium chlorides) systematically gives a much smaller but non-negligible increase in the PL QY. We discuss possible reasons for this result, which points toward a more complex and dynamic QD surface. Finally we show that Z-type metal halide ligand treatments also lead to a strong increase in the PL QY of CdSe, CdS, and InP QDs and can increase the efficiency of sintered CdTe solar cells. These results show that surface anions are the dominant source of trap states in II–VI and III–V QDs and that passivation with Lewis acidic Z-type ligands is a general strategy to fix those traps. Our work also provides a method to tune the PL QY of QD samples from nearly zero up to near-unity values, without the need to grow epitaxial shells.

Structures and thermodynamic stability of cobalt molybdenum oxide (CoMoO4-II)

This contribution reports density functional theory (DFT) calculations on structural and electronic properties of bulk and surfaces of cobalt molybdenum oxide CoMoO4-II; i.e., a material that enjoys a wide array of chemical catalytic and optical applications. Estimated lattice constants and atomic charges for bulk CoMoO4-II reproduce limited analogous experimental measurements. Bader's charges confirm the ionic nature for metal-O bonds in bulk and surfaces of CoMoO4-II. Plotted partial density of states reveal a narrow band gap of 1.8 eV for bulk CoMoO4-II. We found that cleaving bulk of CoMoO4-II along the low-Miller indices afford twelve distinct surfaces. Upward displacement of oxygen atom becomes evident when contrasting bulk positioning of atoms with relaxed surfaces. The two mixed Mo/O- and Co/O–terminated surfaces dominate the thermodynamic stability diagram at 1 atm and 300 – 1400 K, and across a wide range of oxygen chemical potential. The presence of surface oxygen atoms in these stable surfaces is expected to facilitate the occurrence of oxygen reduction reactions as experimentally demonstrated. Likewise, the adjacent surface cations (Mo4+/Co2+) and anions (O2−) serve as Lewis-acid pairs; i.e., very potent active sites in prominent catalysis reactions.

Complex Transfer Reaction from ZnO to ZnS Quantum Dots Driven by Surface Anions

This work demonstrates preferential transfer of 8-hydroxyquinoline-5-sulfonic acid (HQS) from surface of ZnO quantum dots to ZnS quantum dots in the form of Zn(QS)2 complex. This is an instance of inter quantum dot complex or Z-type ligand transfer that depends on solvent system—more precisely, solubility of the migrating complex. The migration can be explained using Langmuir model by considering two parallel adsorption equilibria on ZnO and ZnS surfaces. We also propose that higher stability of the zinc quinolato complex on ZnS surface in comparison to that of ZnO is the driving force of the reaction.

Copper-Coupled Electron Transfer in Colloidal Plasmonic Copper-Sulfide Nanocrystals Probed by in Situ Spectroelectrochemistry.

Copper-sulfide nanocrystals can accommodate considerable densities of delocalized valence-band holes, introducing localized surface plasmon resonances (LSPRs) attractive for infrared plasmonic applications. Chemical control over nanocrystal shape, composition, and charge-carrier densities further broadens their scope of potential properties and applications. Although a great deal of control over LSPRs in these materials has been demonstrated, structural complexities have inhibited detailed descriptions of the microscopic chemical processes that transform them from nearly intrinsic to degenerately doped semiconductors. A comprehensive understanding of these transformations will facilitate use of these materials in emerging technologies. Here, we apply spectroelectrochemical potentiometry as a quantitative in situ probe of copper-sulfide nanocrystal Fermi-level energies ( EF) during redox reactions that switch their LSPR bands on and off. We demonstrate spectroscopically indistinguishable LSPR bands in low-chalcocite copper-sulfide nanocrystals with and without lattice cation vacancies and show that cation vacancies are much more effective than surface anions at stabilizing excess free carriers. The appearance of the LSPR band, the shift in EF, and the change in crystal structure upon nanocrystal oxidation are all fully reversible upon addition of outer-sphere reductants. These measurements further allow quantitative comparison of the coupled and stepwise oxidation/cation-vacancy-formation reactions associated with LSPRs in copper-sulfide nanocrystals, highlighting fundamental thermodynamic considerations relevant to technologies that rely on reversible or low-driving-force plasmon generation in semiconductor nanostructures.

Surface reconstruction of fluorites in vacuum and aqueous environment

Surfaces and interfaces of bulk materials with liquids are of importance for a wide range of chemical processes. In this work, we systematically explore reconstructions on the (100) surface of calcium fluoride $({\mathrm{CaF}}_{2})$ and other fluorites $(M{\mathrm{F}}_{2})$, $M={\text{Sr},\text{Cd},\text{Ba}}$ by sampling the configurational space with the minima hopping structure prediction method in conjunction with density functional theory calculations. We find a large variety of structures that are energetically very close to each other and are connected by very low barriers, resulting in a high mobility of the topmost surface anions. This high density of configurational states makes the ${\mathrm{CaF}}_{2}$ (100) surface a very dynamic system. The majority of the surface reconstructions found in ${\mathrm{CaF}}_{2}$ are also present in ${\mathrm{SrF}}_{2},{\mathrm{CdF}}_{2}$, and ${\mathrm{BaF}}_{2}$. Furthermore, we investigate in detail the influence of these reconstructions on the crystal growth of ${\mathrm{CaF}}_{2}$ in solvents by modeling the fluorite-water interface and its wetting properties. We perform a global structural search both by explicitly including water molecules and by employing a recently developed soft-sphere solvation model to simulate an implicit aqueous environment. The implicit approach correctly reproduces both our findings with the explicit-water model and the experimentally reported contact angles for the partial-hydrophobic (111) and hydrophilic (100) surfaces. Our simulations show that the high anion mobility and the low coordination of the (100) surface atoms strongly favors the adsorption of water molecules over the (111) surface. The aqueous environment makes terminations with low-coordination surface atoms more stable, promoting (100) growth instead of the (111).

Production, characterization and evaluation of biochar from pod (Pisum sativum), leaf (Brassica oleracea) and peel (Citrus sinensis) wastes

Biochar has potential as a valuable tool for the agricultural industry with its unique ability to help build soil health, increase physical properties of soil, soil pH, organic carbon content, conserve water and mitigate drought, reduce GHG emission, conserve nutrients, decrease fertilizer requirements, sequester carbon, increase crop productivity and serve as a most preferred habitat for microbes. In this study, three perishable biomass wastes viz. Pea pod (Pisum sativum), cauliflower leaves (Brassica oleracea) and orange peel wastes (Citrus sinensis) were carbonized and characterized for differential application. The biomass was subjected to carbonization at different temperatures from 100 to 600 °C for 1 h. Biomass and biochar samples were characterized for proximate (M, VM, FC, Ash), ultimate (CHNS-O), biochemical properties (Ce, He, Li), thermo gravimetric analysis, pH, EC and bulk density. The biochars were also analyzed through SEM and FTIR for identification of pore size and functional groups. The char yield was high in cauliflower leaf (30.16 %), followed by orange peel (25.54 %) and pea pod (21.154 %) at 300 °C. The total organic carbon (11.61 %), total negative surface anions (4.25 mmol H+ eq/g C) and water holding capacity (200 %) were high in pea pod biochar. The SEM images of biochar samples showed plane cleavage surfaces with broken edges. The surface functional groups of all the three biochar samples were hydroxyl, methyl, carboxylic and alkene groups. The pea pod and cauliflower leaf biochar showed higher values of organic carbon, total surface anions, water holding capacity and mineral content and performed as best soil amendment than orange peel biochar. These biochar can be used as an effective medium for increasing soil carbon, irrigation efficiency and efficient disposal of agricultural waste-biomass.