Divalent Pb Research Articles

Magnetic nanocomposite for lead (II) removal from water

A magnetic perovskite-spinel oxide nanocomposite synthesized through a sol–gel self-combustion process is used for the first time as an adsorbent to remove toxic heavy metals (i.e., Pb2+). The synthesized LaFeO3:CoFe2O4 ((LFO)1:(CFO)x) (x = 0.11–0.87) nanocomposites possess good stability, abundant oxygenated active binding sites, and unique structural features, making them suitable for removing divalent Pb2+ ions. Scanning electron microscopy, X-ray diffraction, BET surface area, magnetization measurements, zeta-potential analyses, and X-ray photoelectron spectroscopy were used to analyze the nanocomposites, and their structural changes after Pb2+ ions adsorption. Batch tests confirmed that (LFO)1:(CFO)x efficiently removes Pb2+ from water with a maximum adsorption capacity of 105.96 mg/g. The detailed quantitative study indicates that the interaction of hydroxyl groups with Pb2+ ions occurs through electrostatic interactions and complex formation. We also demonstrate a new ring-magnetic separator system that allows magnetic separation of the toxic ions at a higher speed compared to traditional block magnets. The unique structure, high porosity, large specific surface area, and oxygenated functional groups of (LFO)1:(CFO)x nanocomposites make them promising materials for removal of heavy metal ions and possibly other environmental pollutants. This study provides a new approach to preparing nanocomposites of magnetic spinel ferrites with perovskite oxides for environmental applications.

Photocatalytic Reduction of Cr(VI) and Pb(II) with Biogenically Synthesized Copper Oxide Nanoparticles Using an Extract of the Myriophyllum spicatum Plant

The biogenic synthesis of copper oxide nanoparticles was explored using the Myriophyllum spicatum plant through a process involving co-precipitation and was utilized as an effective photocatalyst for the reduction of Cr(VI) and Pb(II) ions in an aqueous solution. The plant-mediated CuO nanoparticles were characterized using microscopic techniques (TEM and SEM), FT-IR, and XRD analyses. The amount of the reduced metal ions was determined by UV–visible and Atomic Absorption (AA) spectrophotometers. The analyses of the functional group present in the leaf extract revealed the type of bioactive molecules that were involved in the formation of copper oxide nanoparticles. The nanoparticles were used in the photo-enhanced reduction of hexavalent Cr and divalent Pb ions, and the impact of solution pH, initial metal concentrations, and photocatalyst dosage was investigated to establish the optimal performance of the CuO nanoparticles. Results revealed a direct association between the reduction of metal ions and catalyst dosage in both cases. A maximum percentage reduction of 89.2% and 79.1% was achieved for Cr(VI) and Pb(II), respectively, using 3 g of the CuO nanoparticles. This confirms that the CuO nanoparticles exhibited higher efficiency for Cr(VI) reduction as compared to Pb(II) reduction and indicates that CuO nanoparticles are a promising photocatalyst that is capable of reducing these metal ions into less toxic products.

Mechanisms of lead-containing pigment discoloration caused by Naumannella cuiyingiana AFT2T isolated from 1500 years tomb wall painting of China

Biodeterioration of ancient wall paintings is a ubiquitous phenomenon that threatens the long-term survival of invaluable cultural heritage. In this study, the Naumannella cuiyingiana AFT2T, isolated from the surface of tomb paintings dating back 1500 years, was observed to be capable of altering the appearing colors of Pb-containing pigments. By a combination of physiological and biochemical measurements and transcriptomic analysis of strain AFT2T under Pb amendment treatments, the discoloration mechanisms were investigated further in depth. Incubation experiments showed that the discoloration reaction resulted from an interaction between Pb-containing pigments and strain AFT2T cells. Subsequently, we found that strain AFT2T had ability to assimilate Pb ions from pigments by using EDX mapping. Finally, after comparing to the controls, it is speculated that the observed discoloration is the formation of cellular product PbS and a series of additional tests were conducted to verify this. In addition, controlling the chemical composition in the culture medium was utilized to confirm the source of S which might be related to the sulfur-containing amino acids of animal proteins in the medium. Transcriptomic analysis exhibited that Pb stress strongly affected the expression of some genes in strain AFT2T, such as metal ion transport and metabolism genes and genes related to the TlpA family protein disulfide reductases. Among them, the gene of the enzyme with disulfide-bond reducing properties and the gene encoding the divalent Pb ion uptake transporter are the key genes in the process of discoloration. A combination of biochemical reactions and transcriptomic analysis was utilized to reveal the key genes involved in the discoloration of Pb-containing pigments by strain AFT2T. These results provide not only new insights and a theoretical basis for the conservation of cultural relics but also a new means for the management of heavy metal pollution in the environments.

Sorption of metal elements by single-walled carbon nanotubes and x-ray absorption spectroscopy analysis

Single-walled carbon nanotubes (SWCNTs) were used for the sorption of monovalent K(I), divalent Pb(II), Zn(II), and Cd(II) in addition to hexavalent Cr(VI) metal elements from aqueous solutions. X-ray absorption spectroscopy (XAS) was employed for the preliminary characterization of the metals sorbed SWCNTs materials. The adsorption capacities of the investigated metals are associated with the functional groups involved in the sorption mechanism. The sorption and XAS results revealed that hexavalent Cr(VI) was highly adsorbed by SWCNTs. The sorption mechanism of Cr(VI) is associated with the reduction of Cr(VI) to trivalent Cr(III). XAS also suggested that in the environment nearest to the sorbed metals Cr, Pb, Zn, and K, the existing binding interactions are Cr–O, Pb–O, Zn–O, and K–O respectively.

Compressive strength and heavy metal adsorption of cork residue, natural zeolite, and low-grade metakaolin-based geopolymers

Low-grade Portuguese metakaolin (MK), natural zeolite and waste cork residue were tested as replacements for commercial MK-based geopolymers in terms of compressive strengths and heavy metal adsorption properties. The low-grade kaolins were sourced from the Alvarães (A) and Barqueiros (B) deposits in Portugal. Various sets of geopolymers were obtained by replacing MK with up to 75 wt% zeolite and adding cork residue, 20 wt% of the total powder mass, to all geopolymers (A25-C, B25-C – 25 % MK 75 % zeolite; A50-C, B50-C – 50 % MK 50 % zeolite; A75-C, B75-C − 75 % MK 25 % zeolite; A100-C, B100-C – 100 % MK). To keep the environmental footprint of the chemicals to a minimum, the Na2O/Al2O3 and SiO2/Al2O3 molar ratios were kept at 1. Geopolymers were characterized to understand the influence of different ratios of MK and zeolite and also cork residue incorporation on their structure and surface morphology. The crystallinity of the geopolymers increased with increasing zeolite in the structure. The addition of cork residue appeared to yield compact geopolymer materials. Maximum compressive strengths of 26.7 and 25.3 MPa were obtained for Alvarães and Barqueiros MK geopolymers, respectively, with only MK and cork residue in the structure, indicating that zeolite addition does not improve the compressive strength values. The adsorption of divalent Pb2+, Cd2+, Cu2+ and Zn2+ cations and the trivalent Cr3+ cation indicated high adsorption capacities of Portuguese MK-based geopolymers. The adsorption of the cations is dependent on the composition of the geopolymers yielding selective adsorption. The geopolymers adsorb Pb2+ in the highest amounts followed by Cd2+ and Cu2+. Zn2+ is adsorbed in slightly lower amounts and Cr3+ is adsorbed in the least amounts. The cork residue and zeolite appear to significantly affect the structure, morphology and properties of geopolymers Overall, the Portuguese MK geopolymers containing cork residue can be effective replacements for commercial MK geopolymers.

Recent Advancements in Halide and Oxide Double Perovskites as Heterogeneous Photocatalysts for Solar-Driven Photocatalytic Water Splitting and CO2 Reduction

With many intriguing advantages, including cost-effective and outstanding optoelectronic properties such as high carrier mobility, low exciton binding energy, suitable band structure, and long carrier lifetime, all-inorganic lead-based halide perovskites (LHPs) have elicited great interest in optoelectronic fields, particularly in the photocatalysis field. However, the high toxicity and notorious instability of LHPs upon exposure to moisture, light, oxygen, and heat are significant barriers to their practical applications, prompting the development of stable lead-free perovskites. Among the various strategies, the chemical transmutations of two divalent Pb[Formula: see text] ions into one monovalent and one trivalent to form metal halide double perovskites (MHDPs) and their analogous metal oxide double perovskites (MODPs) have emerged as promising alternatives to replace the LHPs owing to their intrinsic chemical stability, eco-friendliness, comparable optoelectronic properties to the LHPs, and high catalytic activity. In this review, we elaborately discuss the recent advancements in MHDP and MODP semiconductor photocatalysts by briefly introducing their underlying fundamentals, such as history, chemical configurations, crystalline structures, electronic structures, and optical properties. Subsequently, we emphasize their contemporary applications in photocatalytic water splitting and CO2 reduction. Finally, we outline some perspectives and challenges in developing MHDPs and MODPs. We anticipated that this review might shed light on designing stable and efficient MHDP and MODP semiconductor photocatalysts for a wide range of solar applications.

Divalent Lead in Aqueous Solution Changes the Surface Morphology of Dolomite and Inhibits Dissolution

In groundwater systems, heavy metal ions as solutes (e.g., Pb) can adsorb onto the surface of calcite group rocks and influence their dissolution processes. The dolomite surface was examined using field emission scanning electron microscopy (SEM) and various characterization tools and the changes in water chemistry indexes were reviewed throughout the dissolution process. Pb adsorption on the dolomite surface was evident after 15 days of exposure to 1 mg/L or 50 mg/L divalent Pb salt solutions; the Pb surface phase was mainly PbCO3 with an octahedral ligand structure. SEM images show that dolomite in divalent Pb salt solutions can lead to the surface morphology exhibiting curved dissolution steps. In the closed system with Pb (1 mg/L), the total alkalinity and conductivity of the solution were lower than in the Pb-free system, and the pH difference was slight, indicating that the dibasic metal ion Pb inhibited the dolomite dissolution process. Combined with the composition of the final solid phase, it is suggested that the dolomite surface preferentially adsorbs Pb2+ on the active sites and that the newly grown solid phase is PbCO3 possesses an octahedral ligand structure. Part of the surface-active site is occupied, resulting in a change in the dissolution profile, and thus preventing further development of the dissolution profile. Ultimately, the entire dolomite surface area is prevented from dissolution. The results of this study suggest that Pb2+ may be an effective inhibitor of dolomite dissolution and may help to further refine the geological carbon sink.

Reduction of Nonradiative Loss in Inverted Perovskite Solar Cells by Donor-π-Acceptor Dipoles.

Inverted perovskite solar cells (IPSCs) attract growing interest because of their simple configuration, reliable stability, and compatibility with tandem applications. However, the power conversion efficiency (PCE) of IPSCs still lags behind their regular counterparts, mainly due to the more serious nonradiative loss. Here, we design three donor-π-acceptor (D-π-A) dipoles with various dipole moments to introduce extra electric fields at the interface of perovskites and electron transport materials via the binding between the carboxylate end group and under-coordinated divalent Pb. The chemical binding reduces the recombination centers, while the superposition of the built-in electric field facilitates the electron collection and the hole blocking. As a result, the nonradiative loss is diminished as the dipole moments of D-π-A dipoles increase, which contributes to a PCE of 21.4% with enhancement in both the open-circuit voltage and fill factor. The stability for an unencapsulated device is also improved due to the hydrophobic property of D-π-A dipoles.

Broadening the optimum thermoelectric power generation range of p-type sintered Bi0.4Sb1.6Te3 by suppressing bipolar effect

Bi2Te3-based compounds are well-known commercial thermoelectric materials near room temperature. However, the strong intrinsic excitations above 400 K severely deteriorate the ZT values and limit the applications of thermoelectric power generation. Here, we choose divalent Pb as an acceptor impurity to improve the thermoelectric performance of p-type Bi0.4Sb1.6Te3 sintered materials at higher temperature. Tiny Pb doping not only obviously suppresses the bipolar effect by increasing the hole concentrations, but also decreases the lattice thermal conductivity via introducing phonon scattering centers, such as grain boundaries, dislocations, and dislocation strains. Consequently, a peak ZT of 1.2 at 375 K and a ZTave of 1.1 from 300 to 500 K are realized. A thermoelectric module comprised of our Bi0.4Sb1.597Pb0.003Te3 and commercial Bi2Te2.5Se0.5 is constructed and the evaluated energy conversion efficiency can reach 5.1 % under a temperature difference of 200 K. This study demonstrates that tiny Pb-doped Bi0.4Sb1.6Te3 is promising for low-grade heat recovery.

Comparison of Physicochemical Properties of Fly Ash Precursor, Na-P1(C) Zeolite-Carbon Composite and Na-P1 Zeolite-Adsorption Affinity to Divalent Pb and Zn Cations.

Considering the growing needs of environmental remediation, new effective solutions should be sought. Therefore, the adsorbed amounts of heavy metal ions, such as lead(II) and zinc(II), on the surface of high-carbon fly ash (HiC FA), zeolite-–carbon composite (Na-P1(C)) and pure zeolite (Na-P1), were investigated. The applied solids were characterized using the following techniques: XRD, SEM-EDS, TEM, porosimetry, SLS, electrophoresis and potentiometric titration. The heavy metal concentration in the probes was determined by applying ICP-OES spectroscopy. Adsorption/desorption and electrokinetic measurements were performed in the systems containing one or two adsorbates. The obtained results indicated that Pb(II) ions are adsorbed in larger amounts on the investigated solid surface due to the molecular sieving effect. The largest adsorption capacity relative to lead(II) ions was observed for pure Na-P1 zeolite (407 mg/g). The simultaneous presence of Pb(II) + Zn(II) mixed adsorbates minimally affects the amount of adsorbed Pb(II) ions and causes a significant decrease of Zn(II) ion adsorption (in comparison with analogous systems containing single adsorbates). It was also shown that all solids can be efficiently regenerated using hydrochloric acid. Thus, the selected pure zeolite can be successfully applied in soil remediation or other purifying technologies as an effective Pb(II) adsorbent.

Amidoxime modified chitosan based ion-imprinted polymer for selective removal of uranyl ions

Ion-imprinting strategy was utilized in the development of UO2(II) imprinted amidoxime modified chitosan sorbent (U-AOCS) that can selectively remove UO2(II) from water. First, cyanoactic acid was linked to the chitosan –NH2 groups and then the inserted –CN groups were converted into amidoxime moieties, which chelate the UO2(II) ions and then the polymer chains were cross-linked by glyoxal. The UO2(II) ions have been then eluted leaving their matching recognition sites. The prepared U-AOCS along with the control NIP displayed maximum capacities toward the UO2(II) ions around 332 and 186 mg/g, respectively, and the isotherms were interpreted better by the Langmuir model in both adsorbents. Moreover, the selective uptake of the uranyl ions in multi-ionic aqueous solutions containing the tetravalent Th(IV) ions, trivalent Al(III), Eu(III), and Fe(III) ions, beside the divalent Pb(II), Co(II), Ni(II), Cu(II) ions confirmed the successful creation of a considerable UO2(II) ions selectivity in the U-AOCS construction. In addition, the U-AOCS adsorbent displayed economic feasibility by maintaining around 95 % of its initial efficiency after the regeneration and reuse for 5 adsorption/desorption cycles.

Band structure and absorption spectra of NH4XI3 (X = Pb, Mg) based hybrid Perovskite for UV ray protector and electrochromic materials applications

Modeling Perovskite materials and tuning their properties by monovalent or divalent cations substitution produce several choice Perovskite compounds, studied extensively to improve the power conversion efficiency, reduce toxicity, and enhance stability. We modeled NH4PbI3 and NH4MgI3 from the parent compound CH3NH3PbI3, by replacing the monovalent CH3NH3+ with NH4+ and the divalent Pb atom with Mg. In this study, the electronic band structure, as well as the electronic bandgaps, were calculated using the Perdew-Burke-Enzenhoff (PBE) and Perdew-Burke-Enzenhoff for solid (PBEsol) exchange-correlation functionals of the Density-functional Theory (DFT) and GW quasiparticle method of the Many-Body Perturbation Theory (MBPT). Similarly, we used Time-Dependent Density Functional Perturbation Theory (TDDFPT) and the solution of the Bethe-Salpeter equation (BSE) of the Many-Body Perturbation Theory to determine the real and imaginary dielectric tensors with and without spin-orbit coupling (SOC). Direct bandgaps at R high symmetry point were reported for NH4PbI3, while NH4MgI3 showed indirect bandgaps at Γ→R high symmetry points with lower bandgaps compared to NH4PbI3. The projected density of state around the Fermi level reveals that the iodine (I) p orbital is most responsible for the valence band in both NH4PbI3 and NH4MgI3, while the Lead (Pb) p orbital and the Magnesium (Mg) s orbitals, show the most prominent contribution to the Conduction bands. Similar Optical spectra were achieved with BSE-SOC, TDDFPT, and TDDFPT-SOC for NH4PbI3 without the absorption onsets, while NH4PbI3 predicts higher values of absorbance and absorption coefficient compared to NH4MgI3 which predict lower reflectivity and higher transmittance. Both compounds show maximum absorption coefficient in the order of 105 in the ultraviolet region like CH3NH3PbI3 and silicon. Therefore, we suggest that NH4PbI3 will be useful as solar cell absorber and UV ray protector, while NH4MgI3 would have more applications in the production of electrochromic materials.

Designed assembly of Ni/MAX (Ti3AlC2) and porous graphene-based asymmetric electrodes for capacitive deionization of multivalent ions

The contamination of aquatic ecosystems by fluoride and heavy metal ions constitute an environmental hazard and has been proven to be harmful to human health. This study explores the feasibility of using asymmetric capacitive deionization (CDI) electrodes to remove such toxic ions from wastewater. An asymmetric CDI cell was fabricated using 2D Ni/MAX as an anode and 3D porous reduced graphene oxide (pRGO) as a cathode for the electrosorption of F−, Pb2+, and As(III) ions. A simple microwave process was used for the synthesis of Ni/MAX composite using fish sperm DNA (f-DNA) as a cross-linker between MAX nanosheets (NSs) and the metallic Ni nanoparticles (NPs). Further, pRGO anode was prepared through effective reduction of RGO using lemon juice as green reducing agent with the assist of f-DNA as a structure-directing agent for the formation of 3D network. With this tailored nanoarchitecture, pRGO and Ni/MAX electrodes exhibited a high specific capacitance of 760 and 385 F g−1, respectively. The fabricated Ni/MAX and pRGO based CDI system demonstrated a high electrosorption capacity of 68, 76, and 51 mg g−1 for the monovalent F−, divalent Pb2+, and trivalent As(III) ions at 1.4 V in neutral pH. Furthermore, Ni/MAX//pRGO system was successfully applied for the removal of total F(T), Pb(T), and As(T) ions from real industrial wastewater and contaminated groundwater. The present findings indicate that the fabricated Ni/MAX//pRGO electrode has excellent electrochemical properties that can be exploited for the removal of anionic and cationic metal ions from aqueous solutions in a CDI based system.

Enhanced Visible Light Absorption in Layered Cs3Bi2Br9 Halide Perovskites: Heterovalent Pb2+ Substitution-Induced Defect Band Formation

We have successfully substituted trivalent Bi3+ with divalent Pb2+ in Cs3Bi2Br9-layered perovskites. Controlled heterovalent Pb substitution in these Cs3Bi2Br9-layered perovskites reduces the band gap because of the emergence of defect states in between the bands. These heterovalent Pb-substituted Cs3Bi2Br9 bulk perovskite compounds are successfully synthesized for the first time by chemical reprecipitation method. X-ray photoelectron spectroscopy analysis indicate that lead substitution in the structure is in Pb2+ form, which creates a charge imbalance in the compound as it replaces Bi3+ from the layered perovskite structure. Such charge imbalance is compensated either by bromine vacancies (VBr) or interstitial cesium (Csi) additions. VBr or Csi in Cs3Bi2Br9 along with PbBi creates defect states in between the bands, which results in redshift in the layered perovskite band. Band structure calculations indeed confirm the onset of such defect states, responsible for the redshift. A more detailed defect physics simulation indicates that the defect complex PbBi + VBr is more probable to form if Pb is rich in the environment, which consequently introduces a few deep level defects responsible for the reduction of the band gap. Understanding of the electronic structure and defect physics of such heterovalent Pb-substituted Cs3Bi2Br9 will strengthen the future photovoltaic and optoelectronic applications.

Synergetic Tuning of the Electrical and Thermal Transport Properties via Pb/Ag Dual Doping in BiCuSeO

The influence of Pb/Ag dual doping on the thermoelectric performance of BiCuSeO was investigated. It reveals that the electrical conductivity can be obviously improved owing to the increased carrier concentration mostly caused by the divalent Pb2+ doping at trivalent Bi3+. The electrical conductivity improves from 7.29 S/cm for BiCuSeO to 397.40 S/cm for Pb0.06Bi0.94Cu0.94Ag0.06SeO and Pb0.06Bi0.94CuSeO at 327 K. Combined with the moderate Seebeck coefficient (>120 μV/K) due to the large effective mass, a large power factor with 834 μW/mK2 is achieved. Meanwhile, the lattice thermal conductivity is visibly decreased, mainly benefiting from the substitution of Ag+ at the Cu+ site since the phonon scattering can be enhanced by mass fluctuation and strain fluctuation between the two elements. Thus, the total thermal conductivity is suppressed effectively compared with the Ag-free sample Pb0.06Bi0.94CuSeO. Finally, a maximum ZT value with nearly 1.0 has been obtained for Pb0.06Bi0.94Cu0.94Ag0.06SeO at 873 K, which is ∼64% and ∼47% larger than those of the pristine sample BiCuSeO and Ag-free sample Pb0.06Bi0.94CuSeO. Additionally, the ZT is also larger than the maximum value for the reported Pb-free samples BiCu0.94Ag0.06SeO and Bi0.92Ag0.08CuSeO, suggesting Pb and Ag are effective codopants of BiCuSeO to synergetically tune its electrical and thermal transport properties.

Divalent doping-induced thermoelectric power factor increase in p-type Bi2Te3 via electronic structure tuning

We use first-principles calculations to reveal the effects of divalent Pb, Ca, and Sn doping of Bi2Te3 on the band structure and transport properties, including the Seebeck coefficient, α, and the reduced power factor, α2σ/τ, where σ is the electrical conductivity and τ is the effective relaxation time. Pb and Ca additions exhibit up to 60%–75% higher peak α2σ/τ than that of intrinsic Bi2Te3 with Bi antisite defects. Pb occupancy and Ca occupancy of Bi sites increase σ/τ by activating high-degeneracy low-effective-mass bands near the valence band edge, unlike Bi antisite occupancy of Te sites that eliminates near-edge valence states in intrinsic Bi2Te3. Neither Pb doping nor subatomic-percent Ca doping increases α significantly, due to band averaging. Higher Ca levels increase α and diminish σ, due to the emergence of a corrugated band structure underpinned by high-effective-mass bands, attributable to Ca–Te bond ionicity. Sn doping results in a distortion of the bands with a higher density of states that may be characterized as a resonant state but decreases α2σ by up to 30% due to increases in the charge carrier effective mass and decreases in both spin–orbit coupling and valence band quasidegeneracy. These results, and thermal conductivity calculations for nanostructured Bi2Te3, suggest that Pb or Ca doping can enhance the thermoelectric figure of merit ZT to values up to ZT ∼ 1.7, based on an experimentally determined τ. Our findings suggest that divalent doping can be attractive for realizing large ZT enhancements in pnictogen chalcogenides.

More effective immobilization of divalent lead than hexavalent chromium through carbonate mineralization by Staphylococcus epidermidis HJ2

Heavy metals are the most common pollutant of soil and water, and are being the center of attention due to their toxicity and carcinogenic nature for environment and human health. Microbially induced carbonate precipitation (MICP) is one of well-known processes in recent years for metals immobilization; however, it could have preference for divalent metal ions as MICP directly precipitates calcium ions. Thus, the present research mainly focused on the MICP for the remediation of divalent Pb(II) and hexavalent Cr(VI) in solution using ureolytic Staphylococcus epidermidis. The urease activity led to the metal removal in MICP process, and the removal efficiency of Pb(II) and Cr(VI) was up to 86% and 76.8% (with initial metals concentration 25 mg l−1), respectively. The FTIR spectra revealed number of peaks indicative of CO3 bonding and formation of carbonate compounds in MICP samples; however, such peaks were clearly identified in MICP-Pb than MICP-Cr(VI) due to direct precipitation or immobilization ability of similar valency (Ca2+ and Pb2+). The SEM images also showed the deposition contained metals produced by co-precipitation with calcium clearly. The results showed significant difference in terms of Cr(VI) – and Pb(II) – immobilization, and MICP depicted clear efficacy or preference in the immobilization of divalent over multivalent metal ions.

Lead‐Free Metal Halide Perovskite Nanocrystals: Challenges, Applications, and Future Aspects

AbstractLead halide perovskite materials have shown strong promise in energy harvesting and generation over the past five years. However, their poor ambient stability and lead toxicity issues hinder optoelectronic applications. In the quest for alternatives, metal halide perovskites with lower toxicity and more stable metals have recently emerged. The divalent Pb2+ could be replaced with isoelectronic Sn2+, but Sn2+ tends to oxidize rapidly in presence of air to Sn4+, forming a defect in the structure. However, Sn2+‐based perovskites have been stabilized in 2D structures. Recently Sn4+ based halide perovskites nanocrystals with have been reported with poor luminescence. The replacement of Pb2+ with isoelectronic trivalent elements (Sb3+, Bi3+) results in A3B2X9 type defect‐order perovskite structure, which shows promises for optoelectronic applications. The perovskite nanocrystals of Sb, Bi have been reported in the form of dimers and layered structures. In addition to these, double perovskites, where two divalent Pb2+ are replaced with a monovalent and a trivalent cation have been reported very recently. In this Focus Review, we give a brief summary of different non‐lead perovskite nanocrystals starting from synthesis, characterization, stability, properties to applications, along with potential future directions.

Protonema of the moss Funaria hygrometrica can function as a lead (Pb) adsorbent.

Water contamination by heavy metals from industrial activities is a serious environmental concern. To mitigate heavy metal toxicity and to recover heavy metals for recycling, biomaterials used in phytoremediation and bio-sorbent filtration have recently drawn renewed attention. The filamentous protonemal cells of the moss Funaria hygrometrica can hyperaccumulate lead (Pb) up to 74% of their dry weight when exposed to solutions containing divalent Pb. Energy-dispersive X-ray spectroscopy revealed that Pb is localized to the cell walls, endoplasmic reticulum-like membrane structures, and chloroplast thylakoids, suggesting that multiple Pb retention mechanisms are operating in living F. hygrometrica. The main Pb-accumulating compartment was the cell wall, and prepared cell-wall fractions could also adsorb Pb. Nuclear magnetic resonance analysis showed that polysaccharides composed of polygalacturonic acid and cellulose probably serve as the most effective Pb-binding components. The adsorption abilities were retained throughout a wide range of pH values, and bound Pb was not desorbed under conditions of high ionic strength. In addition, the moss is highly tolerant to Pb. These results suggest that the moss F. hygrometrica could be a useful tool for the mitigation of Pb-toxicity in wastewater.

Design of Lead-Free Inorganic Halide Perovskites for Solar Cells via Cation-Transmutation.

Hybrid organic-inorganic halide perovskites with the prototype material of CH3NH3PbI3 have recently attracted intense interest as low-cost and high-performance photovoltaic absorbers. Despite the high power conversion efficiency exceeding 20% achieved by their solar cells, two key issues-the poor device stabilities associated with their intrinsic material instability and the toxicity due to water-soluble Pb2+-need to be resolved before large-scale commercialization. Here, we address these issues by exploiting the strategy of cation-transmutation to design stable inorganic Pb-free halide perovskites for solar cells. The idea is to convert two divalent Pb2+ ions into one monovalent M+ and one trivalent M3+ ions, forming a rich class of quaternary halides in double-perovskite structure. We find through first-principles calculations this class of materials have good phase stability against decomposition and wide-range tunable optoelectronic properties. With photovoltaic-functionality-directed materials screening, we identify 11 optimal materials with intrinsic thermodynamic stability, suitable band gaps, small carrier effective masses, and low excitons binding energies as promising candidates to replace Pb-based photovoltaic absorbers in perovskite solar cells. The chemical trends of phase stabilities and electronic properties are also established for this class of materials, offering useful guidance for the development of perovskite solar cells fabricated with them.