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FESEM image of the intermediate product after 2 min of HCl addition (A), HRTEM image (B to D) and the corresponding SAED pattern (inset in B) showing δ-MnO 2 nanoparticles. The red contour in the particles indicates that they are hexagonal.
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Birnessite (layer type Mn(III, IV) oxides with ordered sheet stacking) is the most common mineral species of manganese (Mn) oxides, and has been demonstrated to be among the strongest sorbents and oxidants in surface environments. The morphology of birnessite is one of the key factors affecting its reactivity. Either biotic or abiotic birnessite sa...
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... subordinate high-energy surfaces became the highest- energy surfaces. 4 Thus, OA may occur sequentially at these surfaces. Although data for the surface energy of birnessite have not been reported, the surface energies of the (001) and (100) planes can be compared using the law of Bravais and the growth theory of Gibbs-Wulff. 71,72 The main principle of the law of Bravais is that the final shape of the crystal should consist of crystal facets with the largest surface atomic densi- ties. According to the growth theory of Gibbs-Wulff, if the to- tal energies of crystal surfaces are minimal, the crystal as- sumes its equilibrium shape and the growth rate of crystal facets is proportional to the crystal surface energies. In our results, the (001) surface area and surface atomic densities of the birnessite nanoflowers are much larger than those of the (100) plane. Therefore, we deduced that the edge-to-edge OA process occurs before the face-to-face OA process, because the surface energy of the (100) plane is larger than that of the (001) plane. Interestingly, Portehault and coworkers proposed, through observation of nanoflower slices, that nanoflowers had a core-shell architecture. 20 The diameters of the cores of their birnessite samples, formed during the initial stages of the re- dox reaction between MnSO 4 and excess KMnO 4 at room tem- perature, were about 200 nm. Meanwhile, in our study, a small amount of HCl reacted with excess KMnO 4 at 105 °C, and the diameters of the synthesized birnessite nuclei are much smaller (approximately 20 nm, Fig. 2A). Vigorous Brownian motion occurs at a higher temperature, and a small number of nanoparticles are produced with less HCl reactant, which could be responsible for the smaller nuclei of birnessite nanoflowers formed in the initial reaction stages of our experiment. 68 These synthetic birnessite samples can be regarded as the closest analogs of birnessite in the environment. 26,27 Never- theless, complex environmental parameters, such as co- existing ions, organic matter, microorganisms and minerals, could greatly impact or even change the crystal growth pro- cess of Mn oxides in nature. [21][22][23][24][25][26][27]54,60,61 Further investigations into the effect of environmental parameters on the growth process of birnessite crystals are thus ...
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... 2 min of reaction, primary nanoflakes were observed by HRTEM (Fig. 2B-D). The SAED pattern in the inset of Fig. 2B reveals that the nanoflakes were poorly crystalline at this stage. Each side of the primary nanoflakes ranges from 2 to 4 Fig. S4. † The FESEM image of nanoparticles without sonication shows that these nanoflakes are associated with the formation of larger aggregates with a diameter of about 20 nm ( Fig. 2A). As KMnO 4 continuously reacted with HCl, newly formed poorly crystalline nanoflakes were generated and assembled with these aggregates. The aggregates in Fig. 3A exhibit a rough texture with a radius of ∼75 nm, with ultra-thin nano- petals that grow epitaxially from the cores detected by TEM imaging (Fig. S3A & B †). (Fig. S3B †). In another region, there are small nanoflakes that aggregate on the nuclei (Fig. 3B) and have some degree of orientation with the same d hkl spacing of 0.24 nm corresponding to the (100) birnessite faces ( Fig. 3C and D). However, these lattice fringes are ran- domly oriented within the viewing plane. The HRTEM image in Fig. 3C shows that four blocks of δ-MnO 2 nanoflakes at- tach to each other to form nanopetals. 62 This is consistent with the observations of such δ-MnO 2 -like hexagonal nanoflakes at the initial stages of cryptomelane formation. 60 Primary nanoflake-like blocks may assemble into birnessite and/or cryptomelane under different conditions. The OH − is reduced ...
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... 2 min of reaction, primary nanoflakes were observed by HRTEM (Fig. 2B-D). The SAED pattern in the inset of Fig. 2B reveals that the nanoflakes were poorly crystalline at this stage. Each side of the primary nanoflakes ranges from 2 to 4 Fig. S4. † The FESEM image of nanoparticles without sonication shows that these nanoflakes are associated with the formation of larger aggregates with a diameter of about 20 nm ( Fig. 2A). As KMnO 4 continuously reacted with HCl, newly formed poorly crystalline nanoflakes were generated and assembled with these aggregates. The aggregates in Fig. 3A exhibit a rough texture with a radius of ∼75 nm, with ultra-thin nano- petals that grow epitaxially from the cores detected by TEM imaging (Fig. S3A & B †). (Fig. S3B †). In another region, there are small nanoflakes that aggregate on the nuclei (Fig. 3B) and have some degree of orientation with the same d hkl spacing of 0.24 nm corresponding to the (100) birnessite faces ( Fig. 3C and D). However, these lattice fringes are ran- domly oriented within the viewing plane. The HRTEM image in Fig. 3C shows that four blocks of δ-MnO 2 nanoflakes at- tach to each other to form nanopetals. 62 This is consistent with the observations of such δ-MnO 2 -like hexagonal nanoflakes at the initial stages of cryptomelane formation. 60 Primary nanoflake-like blocks may assemble into birnessite and/or cryptomelane under different conditions. The OH − is reduced ...
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... 2 min of reaction, primary nanoflakes were observed by HRTEM (Fig. 2B-D). The SAED pattern in the inset of Fig. 2B reveals that the nanoflakes were poorly crystalline at this stage. Each side of the primary nanoflakes ranges from 2 to 4 Fig. S4. † The FESEM image of nanoparticles without sonication shows that these nanoflakes are associated with the formation of larger aggregates with a diameter of about 20 nm ( Fig. 2A). As KMnO 4 continuously reacted with HCl, newly formed poorly crystalline nanoflakes were generated and assembled with these aggregates. The aggregates in Fig. 3A exhibit a rough texture with a radius of ∼75 nm, with ultra-thin nano- petals that grow epitaxially from the cores detected by TEM imaging (Fig. S3A & B †). (Fig. S3B †). In another region, there are small nanoflakes that aggregate on the nuclei (Fig. 3B) and have some degree of orientation with the same d hkl spacing of 0.24 nm corresponding to the (100) birnessite faces ( Fig. 3C and D). However, these lattice fringes are ran- domly oriented within the viewing plane. The HRTEM image in Fig. 3C shows that four blocks of δ-MnO 2 nanoflakes at- tach to each other to form nanopetals. 62 This is consistent with the observations of such δ-MnO 2 -like hexagonal nanoflakes at the initial stages of cryptomelane formation. 60 Primary nanoflake-like blocks may assemble into birnessite and/or cryptomelane under different conditions. The OH − is reduced ...
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... this stage which is due to agglomeration of the primary nanoflakes to form nuclei, and the SSA increased during the re- action from 2 min to 7 min (Table 1), although the size of ag- gregates also increased at this stage. Yin et al. showed that the agglomeration of crystals to form aggregates (Fig. 2) is the cause of the decrease in SSA. 61 Edge-to-edge OA self-assembly of crystalline primary nanoparticles At the later stage, precipitation of primary nanoflakes and crystal growth of intermediate products occurred continu- ously. When HCl was added to KMnO 4 for 15 min, larger nanoflakes are formed, as shown from the observations of the aggregate surfaces indicated by the red circle in Fig. 4A. Like petals, they grew vertically on the core (Fig. 4B). Al- though most of the aggregates possess a nanoflower-like morphology, one particle in Fig. 4A exhibits a rough sur- face (red-circled area) resembling the surfaces of the parti- cles in Fig. 3A. This observation suggests that the rough textures gradually transform into nanopetals. The diameter of the nanoflowers increased from 75 nm to 176 nm as HCl was continually added from 7 min to 30 min (Fig. 3B, 5A and B). Interestingly, the HRTEM images in . 4C and D show that the (100) birnessite planes in the nanosheets are not oriented exactly in the same way but are better defined at this stage because the randomly ori- ented primary nanoflakes rotate gradually to face the same direction. Moreover, pores are detected within the nano- sheets in Fig. 4D (yellow circle). These pores may be cre- ated by self-assembly of primary nanoflakes, as reported by Ruiz-Agudo et al. 63 In the final stage of aging, the diameter of the nano- flowers increases to 220 nm ( Fig. 6A and B), and the nano- petals which are shown in Fig. 6C and D indicate that the pri- mary nanoflakes have sufficient time to adjust the direction of their lattice, driven by the reduction of surface energy. 64 Thus, the HRTEM image of the sample aged for 24 h at 60 °C clearly shows a perfect crystallographic match (Fig. 6C). Fig. 6C shows four different nanoparticles closely connected edge-to-edge. Three nanoparticles share the same d hkl spacing of 0.24 nm, corresponding to the (100) plane of birnessite. However, only one particle exhibits a clockwise misorientation angle of 29° between the lattice fringes during attachment, resulting in the formation of a defect at the interface (Fig. 6C, yellow rectangle). From 2 min of HCl addi- tion to aging for 24 h, the attenuation rate of the PDF pattern increases, and the distances over which the attenuation is ...
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Citations
... In addition, visible boundaries in the material suggest a growth mechanism of particle attachment. 61 This could be confirmed through the images of TEM ( Figure 1D) and HRTEM ( Figure 1E,F). It was possible to observe that a particle attachment forms the NiO nanoflowers following a self-assembly process. ...
The design and development of efficient and electrocatalytic sensitive nickel oxide nanomaterials have attracted attention as they are considered cost-effective, stable, and abundant electrocatalytic sensors. However, although innumerable electrocatalysts have been reported, their large-scale production with the same activity and sensitivity remains challenging. In this study, we report a simple protocol for the gram-scale synthesis of uniform NiO nanoflowers (approximately 1.75 g) via a hydrothermal method for highly selective and sensitive electrocatalytic detection of hydrazine. The resultant material was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. For the production of the modified electrode, NiO nanoflowers were dispersed in Nafion and drop-cast onto the surface of a glassy carbon electrode (NiO NF/GCE). By cyclic voltammetry, it was possible to observe the excellent performance of the modified electrode toward hydrazine oxidation in alkaline media, providing an oxidation overpotential of only +0.08 V vs Ag/AgCl. In these conditions, the peak current response increased linearly with hydrazine concentration ranging from 0.99 to 98.13 μmol L-1. The electrocatalytic sensor showed a high sensitivity value of 0.10866 μA L μmol-1. The limits of detection and quantification were 0.026 and 0.0898 μmol L-1, respectively. Considering these results, NiO nanoflowers can be regarded as promising surfaces for the electrochemical determination of hydrazine, providing interesting features to explore in the electrocatalytic sensor field.
... Specific regions show fluffy rosettes of platy crystals which are indicative of lithiophorite or birnessite. These clusters of layered manganese minerals appear readily in synthetic and environmental samples and are called "nanoflowers" (Liang et al., 2017). They form in much the same way as nodules and may be a precursor for the latter's development. ...
Manganese-oxides are one of nature’s strongest sorbents and oxidants which often occur in trace amounts in soils as amorphous coatings and crusts. Thus, not much is known about their microscale mineralogy in soils and concretions. We collected soils enriched in pedogenic manganese-oxides and concretions from Graskop, South Africa to determine the mineralogy of naturally occurring manganese phases from soils with varying degrees of pedogenic alteration. Bulk X-ray diffraction (XRD) demonstrates the dominance of lithiophorite and the presence of todorokite in the less altered wad soil compared to the more pedogenically altered soils enriched in gibbsite and birnessite. The mineralogy inside concretions is elucidated with synchrotron µXRD paired with X-ray fluorescence (XRF). Synchrotron XRF mapping shows critical insight into the mechanisms stabilizing manganese and iron in these dolomite-derived yet acid soils. Manganese and calcium are found in consistent ratios in the solum and nodules, and calcium is important for manganese persistence and nodule aggregation/flocculation. Similarly, silicon and iron distribution are strongly correlated, and silica enhances iron stability by altering the crystalline structure and cementing mineral surfaces. The µXRD elucidates the mineralogical gradient across a concretion transect. With birnessite occurring in the outermost layer and todorokite, gibbsite, lithiophorite, and maghemite becoming more abundant in the concretion middle layers. µXRD also indicates mineral phases obscured in the bulk XRD like anatase and ramsdellite and minerals typically from metamorphic or hydrothermal origin including periclase, wüstite, manganosite, and spinel. These novel results quantify the mineralogy and nanoscale distribution of pedogenic manganese-oxides.
... From the TEM analysis, it can be probably inferred that, with the increase in temperature, the Al 2 O 3 nanocrystallites in the aggregate re-arrange to form secondary particles that further coalesce in the same orientation to form the larger crystals and the subsequent coarsening could result in the formation of dense platelets that are observed at 1200 °C. The reduction in the surface energy of the alumina nanocrystallites when they assemble coherently can be considered as the driving force for oriented attachment growth [28][29][30] . A more detailed investigation is required to clearly comprehend the inner mechanism of oriented attachment growth in the formation of alumina platelets. ...
The formation of α-Al2O3 platelets by a bio-templating route using eggshell membranes is investigated. A facile solution soakage method was employed for the synthesis of Al2O3. X-ray diffraction results indicated the Al2O3 phase transformations occurring with the calcination temperature. The growth of α-Al2O3 platelets were carefully studied using scanning and transmission electron microscopes. The biomacromolecules and functional groups present on the eggshell membrane bio-template played a crucial role in the formation of α-Al2O3 platelets. A plausible growth mechanism based on the oriented attachment growth process involving the role of eggshell membrane has been proposed. This study paves the insight for the development of α-Al2O3 anisotropic structures through bio-templated approach
... 13 Examples of knowledge required for these various applications include molecular configurations 14 of intercalated water layers and of their thermal stabilities 4,15 The MnO 2 structure of birnessite is formally composed of stacked sheets of edge-sharing MnO 6 octahedra ( Figure 1) 16−18 and forms ultrathin nanoplatelets with a surface dominated with its basal face. 19,20 It has a formal average oxidation state (AOS) of 4.0, but synthetic and natural forms commonly contain a mixture of Mn oxidation states (Mn IV , Mn III , and Mn II ). 21 −24 In nature, birnessite or vernadite with AOS values as low as ∼3.5 is probably more common because natural organic matter has a strong propensity to reduce Mn IV . ...
Birnessite is a layered MnO2 mineral capable of intercalating nanometric water films in its bulk. With its variable distributions of Mn oxidation states (MnIV, MnIII, and MnII), cationic vacancies, and interlayer cationic populations, birnessite plays key roles in catalysis, energy storage solutions, and environmental (geo)chemistry. We here report the molecular controls driving the nanoscale intercalation of water in potassium-exchanged birnessite nanoparticles. From microgravimetry, vibrational spectroscopy, and X-ray diffraction, we find that birnessite intercalates no more than one monolayer of water per interlayer when exposed to water vapor at 25 °C, even near the dew point. Molecular dynamics showed that a single monolayer is an energetically favorable hydration state that consists of 1.33 water molecules per unit cell. This monolayer is stabilized by concerted potassium–water and direct water–birnessite interactions, and involves negligible water–water interactions. Using our composite adsorption–condensation–intercalation model, we predicted humidity-dependent water loadings in terms of water intercalated in the internal and adsorbed at external basal faces, the proportions of which vary with particle size. The model also accounts for additional populations condensed on and between particles. By describing the nanoscale hydration of birnessite, our work secures a path for understanding the water-driven catalytic chemistry that this important layered manganese oxide mineral can host in natural and technological settings.
... There are numerous reports on (A) building units, (B) growth driving force, and (C) the final evolved hierarchical morphologies following the NCG protocol. Examples of building units shape are (1) PbSe nanocrystals [10], (2) ZnO nanocrystals [13], (3) -MnO 2 nanowires [14], (4) 10-20 nm diameter PbTiO 3 fibers [15], (5) Au spherical seeds [16], (6) 1D-TiO 2 fibers [17], (7) -MnO 2 nanosheets [18], (8) 200-250 nm SnO 2 dodecahedrons [3]. ...
... Similarly, examples of the corresponding growth directing forces are (1) dipolarinteraction [10], (2) orientation specific directional ZnO-ZnO interfacial interaction [13], (3) K + -stabilized ionic interaction [14], (4) surface-electrostatic force [15], (5) laser intense pulses force field [16], (6) electric-field [17], (7) hydrogen-bonding [18], (8) pressure-induced interaction [3]. These lead to the subsequent developed hierarchical morphologies such as (1) PbSe nanowires and nanorings [10], (2) 1D-ZnO nanorods [13], (3) tunneled -MnO 2 nanowires [14], (4) large-sized 3D-PbTiO 3 hollow fibers [15], (5) triangular Au nanoplates [16], (6) multilevel twinned tree-like branched TiO 2 morphologies [17], (7) nanoflowers [18], and (8) µ-sized 3D-ordered SnO 2 superstructures [3], are respectively. ...
... Similarly, examples of the corresponding growth directing forces are (1) dipolarinteraction [10], (2) orientation specific directional ZnO-ZnO interfacial interaction [13], (3) K + -stabilized ionic interaction [14], (4) surface-electrostatic force [15], (5) laser intense pulses force field [16], (6) electric-field [17], (7) hydrogen-bonding [18], (8) pressure-induced interaction [3]. These lead to the subsequent developed hierarchical morphologies such as (1) PbSe nanowires and nanorings [10], (2) 1D-ZnO nanorods [13], (3) tunneled -MnO 2 nanowires [14], (4) large-sized 3D-PbTiO 3 hollow fibers [15], (5) triangular Au nanoplates [16], (6) multilevel twinned tree-like branched TiO 2 morphologies [17], (7) nanoflowers [18], and (8) µ-sized 3D-ordered SnO 2 superstructures [3], are respectively. Importantly the unique morphology of aquatic biominerals and hierarchical motifs is the motivation and basis of the current NCG investigation [19]. ...
The main objectives of the thesis are
1. Investigate biomineralization mimicked nc-ceria individual building units utilized to grow 1D-ceria nanostructures. In this context, de-ionized water (DI-water) having transparent nc-ceria colloidal dispersion with aging leads to anisotropic 1D-ceria nanorods development. Thereby DI-water as an enabler of NCG, similar to aquatic biominerals, is established. To physically demonstrate the building units’ attachment, in-situ TEM e-beam is utilized to act as a probe and also as an enabler of the NCG scheme.
2. Apart from NCG, a significant section is also devoted to investigating the autocatalytic regenerative surface feature of nc-ceria in delivering a tunable charge transfer (CT) visible photoluminescence (PL) emission and quenching.
3. The feasibility of a variety of ultrasonic-sonochemical physio-chemical processes for nanoscience is tracked. Their mechanistic features are accessed, and also utilization in solution-phase material processing is realized.
4. To explore and present ultrasonic-sonochemical process intensification while evaluating the nucleation, growth, and stabilization aspect of the ultrafine oxide-free PVP embedded Al-rich, Al/PVP composite fuel.
5. Lastly, to investigate physically mixed stoichiometric 1:1 NEM made out of the Al/PVP composite fuel and nc-ceria oxidizer. The NEM characteristics evaluated are oxidation, ignition, the energy contained, and also energetics, respectively.
The thesis is organized into six chapters, and the contents of each chapter are described briefly in the following sections.
... After equilibration of HB with Co(II) at pH5 for 24 h, the D values of as-obtained samples, HC5 and HC10, are increased to 7.9 and 8.5 nm respectively. This increase may be the net effects of two opposite contributions: mineral dissolution upon Co(II) adsorption (Manceau et al., 1997) and crystal growth by oriented attachment at low pH (Liang et al., 2017;Marafatto et al., 2018). ...
... In the initial stage of δ-MnO 2 growth, primary nanopetals preferentially undergo edge-to-edge oriented attachment and grow sufficiently large along the a-b plane [42]. Since the hexagonal birnessite layers are rich in negative charges owing to the presence of vacancy sites and Mn(III) in MnO 6 octahedra, hydrated K + or H + in solution adsorb onto the vacancy sites and Mn(III) to balance the negative charges [43]. ...
Engineering MnO2 with rich surface active oxygen species is critical to effectively eliminate formaldehyde (HCHO) under mild conditions. Herein, we introduced a facile redox method to fabricate a series of δ-MnO2 samples by varying the concentration of K⁺, which efficiently modulated the layer size, morphology, crystallinity, redox properties, and thus the surface active oxygen species of the obtained δ-MnO2. The medium potassium concentration led to the optimized MnO bond strength, the abundant surface active oxygen species, and the complete conversion of ca. 22 ppm HCHO at 30 °C under a weight hourly space velocity (WHSV) of 200,000 mL/(gcat h). Surface adsorbed oxygen species (e.g., O2⁻ and O⁻) and surface hydroxyl groups, were suggested to oxidize HCHO into intermediates (i.e., DOM, formate, and carbonate species). Water was critical for further transforming the intermediates into CO2. A Langmuir-Hinshelwood (LH) mechanism was proposed involving in the whole oxidation process.
... Colloidal crystals can be self-assembled from a colloidal suspension by evaporation of the liquid solvent or by gravity sedimentation in a variety of approaches, 7 such as spin coating, 8 vertical deposition, 9,10 electrophoresis, 11,12 centrifugation, 13 freezing, 14 physical confinement, 15 or convective self-assembly 16 to name a few of them. ...
Vertical convective self‐assembly has been extensively used for the preparation of direct photonic crystals, which can be later infiltrated with a more stable material, such as oxide ceramics, by atomic layer deposition. However, the relationship between the self‐assembly parameters of the direct photonic crystals and the optical properties of the inverse opal photonic crystals remains elusive. In this work, the effect of different experimental parameters on the 3D structure and defects density of polystyrene direct photonic crystals produced by vertical convective self‐assembly was assessed. Self‐assembly was investigated using deionized water as media with polymer particles’ concentrations up to 2 mg/mL, temperatures of 40, 50 and 80°C and relative humidity of 45, 70 and 90%. The 3D structure of the resultant direct photonic materials was characterized by the combination of scanning electron microscopy and image analysis, and their optical properties was assessed by reflectance measurements. These results were correlated with the performance of oxide‐based inverse opal photonic crystals produced by the controlled infiltration of the former direct photonic crystals by atomic layer deposition (ALD). It was found that the thickness increased with the concentration of polystyrene particles, while the photonic structure ordering is dependent on the synergy between humidity and temperature. Results also showed higher defects population with increasing evaporation temperature and decreasing relative humidity. This article is protected by copyright. All rights reserved.
... HRTEM was performed on the samples using a JEM-2100F electron microscope operating at 200 kV (resolution in the lattice fringe mode 0.102 nm). 43 HAADF-STEM was performed on the microstructures of the samples at atomic scale using a JEM-ARM200F electron microscope. Thermogravimetric (TG) measurement was performed on DSC200PC/TG209C TG-DSC apparatus. ...
Al-substitution in hematite is ubiquitous in nature and strongly affects the environmental behaviors of hematite. However, the defect microstructure caused by Al-substitution and its inner relationship with the surface reactivity of hematite remain unclear. In this study, the crystal structure of Al-substituted hematite was characterized by high-resolution electron transmission microscopy (HRTEM) and high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Acid-base titration and Pb ²⁺ adsorption experiments were performed to investigate the surface reactivity of Al-substituted hematite. HRTEM images revealed that the proportion of (001) facets on hematite increased from 44.0 ± 3.8% to 84.8 ± 6.5% with increasing Al-substitution. HAADF-STEM images indicated that Al-substitution resulted in more vacancies of Fe atoms on hematite (001) facets. At these Fe defect sites, additional singly (FeOH -0.5 ) and triply (Fe 3 O -0.5 ) coordinated hydroxyl sites were formed. The weight loss due to dehydrogenation was 1.7%, 3.3% and 6.2% with increasing Al-substitution from 0%, 5% to 10%. Besides, the relative percentage of surface oxygen atoms in the surface hydroxyl sites of Al-substituted hematite was consistent with the results of thermogravimetric analysis. At pH 5, the relative charge density of the hematite with 0%, 5% and 10% Al-substitution was 73, 94 and 241 mC m ⁻² , and their adsorption capacity for Pb ²⁺ was 0.82, 1.23 and 3.51 μmol m ⁻² , respectively. These results indicate that the formation of more defect sites with increasing Al-substitution can significantly enhance the surface charge density and Pb ²⁺ adsorption capacity of hematite.
... Synthetic birnessite has generally been used for the removal of hazardous substances [5,76,77]. The synthesis protocols of birnessite vary based on morphology and crystallinity [78]. For instance, amorphous birnessite can be prepared via the method outlined by McKenzie [79], whilst a low crystalline birnessite was prepared by Murray [80] at lower or ambient temperature. ...
Manganese oxides are ubiquitous in soil, sediment and aquatic environment. Over the years, manganese oxides
and their composites have proved to be effective as adsorbents for the removal of metal ions and contaminants
from water/wastewater. Because of their unique chemical and physical properties, they have attracted widespread
attention as excellent adsorbents. This review reports on recent research on the synthesis, characterization,
and application of manganese oxides and their composites for wastewater treatment. The adsorption
characteristics, including experimental conditions and mechanisms involved in the pollutant removal processes,
are discussed. The review provides an overview of the research related to manganese oxides and their application,
including future areas of research and limitations in the current body of research.
