Anion Exchange Mechanism Research Articles

Anion-Exchange Driven Phase Transition in CsPbI3 Nanowires for Fabricating Epitaxial Perovskite Heterojunctions.

Anion-exchange in halide perovskites provides a unique pathway of bandgap engineering for fabricating heterojunctions in low-cost photovoltaics and optoelectronics. However, it remains challenging to achieve robust and sharp perovskite heterojunctions, due to the spontaneous anion interdiffusion across the heterojunction in 3D perovskites. Here, it is shown that the anionic behavior in 1D perovskites is fundamentally different, that the anion exchange can readily drive an indirect-to-direct bandgap phase transition in CsPbI3 nanowires (NWs) and greatly lower the phase transition temperature. In addition, the heterojunction created by phase transition is epitaxial in nature, and its chemical composition can be precisely controlled upon postannealing. Further study of the phase transition dynamics reveals a threshold-dominating anion exchange mechanism in these 1D NWs rather than the gradient-dominating mechanism in 3D systems. The results provide important insights into the ionic behavior in halide perovskites, which is beneficial for applications in solar cells, light-emitting diodes (LEDs), and other semiconductor devices.

Atomistic Insight into the Hydration States of Layered Double Hydroxides.

Effective protective coatings are an essential component of lightweight engineering materials in a large variety of applications as they ensure structural integrity of the base material throughout its whole service life. Layered double hydroxides (LDHs) loaded with corrosion inhibitors depict a promising approach to realize an active corrosion protection for aluminum and magnesium. In this work, we employed a combination of density functional theory and molecular dynamics simulations to gain a deeper understanding of the influence of intercalated water content on the structure, the stability, and the anion-exchange capacity of four different LDH systems containing either nitrate, carbonate, or oxalate as potential corrosion inhibiting agents or chloride as a corrosion initiator. To quantify the structural change, we studied the atom density distribution, radial distribution function, and orientation of the intercalated anions. Additionally, we determined the stability of the LDH systems by calculating their respective hydration energies, hydrogen-bonded network connected to the intercalated water molecules, as well as the self-diffusion coefficients of the intercalated anions to provide an estimate for the probability of their release after intercalation. The obtained computational results suggest that the hydration state of LDHs has a significant effect on their key properties like interlayer spacing and self-diffusion coefficients of the intercalated anions. Furthermore, we conclude from our simulation results that a high self-diffusion coefficient which is linked to the mobility of the intercalated anions is vital for its release via an anion-exchange mechanism and to subsequently mitigate corrosion reactions. Furthermore, the presented theoretical study provides a robust force field for the computer-assisted design of further LDH-based active anticorrosion coatings.

Synthesis of temperature-responsive ionic liquids and study on the behavior and mechanism of Au(III) extraction from hydrochloric acid solutions

For sustainable development and environmental protection, recovery of critical metals, especially for gold, from secondary resources, has recently attracted substantial attention. In this work, two novel temperature-responsive ionic liquids (TRILs), [EA-TMEDA][Tf2N]2 and [EA-TMHDA][Tf2N]2, were designed and firstly synthesized for Au(III) extraction from hydrochloric acid medium. The optimum extraction conditions for Au(III) were selected by optimizing the amount of extractant, acidity and other factors. In optimal conditions, TRILs showed excellent extraction performance for Au(III), which could reach 97.5% with [EA-TMEDA][Tf2N]2 and 91% with [EA-TMHDA][Tf2N]2, respectively. They also exhibited great selectivity in multi-metal solution such as Cu(II), Mn(II) and Co(II). The thermomorphic behaviors were investigated around the upper critical solution temperature (UCST) by the characterization methods of variable-temperature 1H NMR and dynamic light scattering (DLS). The extraction mechanism was also determined as anion exchange mechanism through the maximum metal loading experiments, UV–vis, FT-IR and 13C NMR characterization. In addition, Au(III) could be almost completely stripped by C2H2O4 from the loaded IL phase and there was no significant reduction in efficiency after 5 cycles. Hence, the new TRILs offered outstanding extraction performance for the greener and sustainable extraction of Au(III), and will have broad application prospects in the extraction field.

Extraction and separation on Au(III) and Pt(IV) from HCl media using novel piperazine-based ionic liquid as an ionic exchanger

Selective recovery of gold and platinum from secondary resources is of great significance under the crisis of resource shortage. Hence, the optimal extractant 1-(2-(dimethylamino) ethyl)-4-methyl-piperazin bis(trifluoromethylsulfonyl)imide ([C6-Et-TMEDA-PIP][Tf2N]2) was synthesized and screened out from five piperazine-based ionic liquids (ILs) to construct an IL-water system for Au(III) and Pt(IV) extraction. ILs have high hydrophobicity and low viscosity at room temperature, which can be used as both extractant and hydrophobic phase. The effects of IL dosage, metal concentration and acidity on the extraction efficiency were investigated. Under the optimal conditions, the extraction efficiency of 98.5% (Au(III)) and 97.5% (Pt(IV)) can be achieved. The anion exchange mechanism was verified through the combination of Ultraviolet visible spectroscopy (UV–vis), Nuclear magnetic spectra (NMR) and quantum chemical calculations. Besides that, the two-factor optimization of the extractant dosage and HCl concentration was carried out by Response surface methodology (RSM), and the effective separation of Au(III) and Pt(IV) was successfully achieved. Au(III)/ Pt(IV) was extracted into the IL phase as [Et-TMEDA-PIP+][AuCl4-] and can easily be stripped by reduction to Au(0)/Pt(Ⅱ) with H2C2O4/CS(NH2)2-HCl, and each extraction ability maintained after 5 turns of extraction cycle experiments. Since the excellent behaviors showed in the multi-metal selective extraction and cycle experiments, the [C6-Et-TMEDA-PIP][Tf2N]2 was regarded as the most potential system for Au(III) and Pt(IV) recovery from HCI medium.

On the Potential of a Poly(vinylidenefluoride-co-hexafluoropropylene) Polymer Inclusion Membrane Containing Aliquat® 336 and Dibutyl Phthalate for V(V) Extraction from Sulfate Solutions.

A polymer inclusion membrane (PIM) composed of 50 wt% base polymer poly(vinylidenefluoride-co-hexafluoropropylene), 40 wt% extractant Aliquat® 336, and 10 wt% dibutyl phthalate as plasticizer/modifier provided the efficient extraction of vanadium(V) (initial concentration 50 mg L−1) from 0.1 M sulfate solutions (pH 2.5). The average mass and thickness of the PIMs (diameter 3.5 cm) were 0.057 g and 46 μm, respectively. It was suggested that V(V) was extracted as VO2SO4− via an anion exchange mechanism. The maximum PIM capacity was estimated to be ~56 mg of V(V)/g for the PIM. Quantitative back-extraction was achieved with a 50 mL solution of 6 M H2SO4/1 v/v% of H2O2. It was assumed that the back-extraction process involved the oxidation of VO2+ to VO(O2)+ by H2O2. The newly developed PIM, with the optimized composition mentioned above, exhibited an excellent selectivity for V(V) in the presence of metallic species present in digests of spent alumina hydrodesulfurization catalysts. Co-extraction of Mo(VI) with V(V) was eliminated by its selective extraction at pH 1.1. Characterization of the optimized PIM was performed by contact angle measurements, atomic-force microscopy, energy dispersive X-ray spectroscopy, thermogravimetric analysis/derivatives thermogravimetric analysis and stress–strain measurements. Replacement of dibutyl phthalate with 2-nitrophenyloctyl ether improved the stability of the studied PIMs.

Исследование экстракции висмута (III) производным 1,2,4-триазола из солянокислых растворов

Studied the extraction of bismuth (III from 1.0 mol / l) hydrochloric acid with 1,2,4 triazole derivatives: (1- [2- (2,4-dichlorophenyl) -4-propyl-1 , 3-dioxolan-2-yl] -1H-1,2,4 triazole. Optimum extraction conditions have been found. It has been found that bismuth (III) is extracted by the anion exchange mechanism at a contact time of 5 min. Chlorocomplex of bismuth (III) is isolated and characterized by electron and IR spectroscopy and elemental analysis. Reextraction of bismuth (III) from 1.0 mol / l solution of hydrochloric acid were studied.

Экстракция сурьмы (III) производным 1,2,4-триазола из солянокислых растворов и определение условий отделения Sb (III) от Bi (III)

The extraction of antimony (III) from hydrochloric acid solutions with 1-[2-(2,4-dichlorophenyl)-4- propyl-1,3-dioxolan-2-yl]-1H-1,2,4-triazole was studied. Optimal extraction conditions are found. It is assumed that antimony (III) is extracted by the anion exchange mechanism at a phase contact time of 5 min. The extractable antimo- ny (III) chlorocomplex was isolated and characterized by electron, IR spectroscopy and elemental analysis. The re- extraction and concentration of antimony (III) from hydrochloric acid solutions has been studied. The possibility of separating antimony (III) from bismuth (III) is shown.

Enhanced removal of radioactive iodine anions from wastewater using modified bentonite: Experimental and theoretical study

Efficient and cost-effective removal of radioactive iodine anions from contaminated water has become a crucial task and a great challenge for waste treatment and environmental remediation. Herein, we present hexadecylpyridinium chloride monohydrate modified bentonite (HDPy-bent) for the efficient and selective removal of iodine anions (I− and IO3−) from contaminated water. Batch experiments showed that HDPy-bent could remove more than 95% of I− and IO3− within 10 min, and had maximum I− and IO3− adsorption capacities of 80.0 and 50.2 mg/g, respectively. Competitive experiments indicated that HDPy-bent exhibited excellent I− and IO3− selectivity in the excessive presence of common concomitant anions including PO43−, SO42−, HCO3−, NO3−, Cl− (maximum mole ratio of anions vs iodine anions was ∼50,000). An anion exchange mechanism was proposed for the selective adsorption of iodine anions. Optimal adsorption structure of HDPy+/I− (IO3−) at atomic level and driving forces of the I− (IO3−) adsorption were calculated by density functional theory (DFT) simulations. Moreover, the good durability and reusability of the HDPy-bent has been demonstrated with 5 adsorption-desorption cycles. Dynamic column experiment also demonstrated that HDPy-bent exhibited excellent removal and fractional recovery capabilities towards I− and IO3− from simulated groundwater and environmental water samples. In conclusion, this work presents a promising adsorbent material for the decontamination of radioactive iodine anions from wastewater on a large scale.

Development of Multifunctional CoAl Based Layered Double Hydroxide Protective Film on Aluminum Alloy

A protective CoAl-layered double hydroxide (LDH) thin film was developed directly on the aluminum substrate. Further, the low-surface-energy molecules (1H, 1H, 2H, 2H perfluorododecyl trichlorosilane) were incorporated inside the LDH network through an anion exchange mechanism to obtain a superhydrophobic CoAl-LDH surface. The developed films were characterized by scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR), and additional contact angle measurements were made to evaluate the superhydrophobicity of modified CoAl-LDHs against different solutions. The water contact angle (WCA) of the modified CoAl-LDH surface was observed to be about 153° and remained sufficiently stable after long-term immersion in NaCl solution. The effect of excessive ultrasonication on film structural variations and superhydrophobicity was also analyzed for outdoor applications. The high charge transfer resistance observed from the analysis of long-term electrochemical impedance spectroscopy (EIS) indicates the significant corrosion-resistance properties of the developed CoAl-LDHs. This research on protective CoAl-LDHs will bring insights into the understanding of new aspects of surface protection and implementation in many engineering applications.

Preparation, characterization and antibacterial applications of ZnAl- LDH with the diaminododecylphosphonic acid intercalation

Layered double hydroxides (LDHs) have been widely investigated in a wide range of applications in health, in the pharmaceutical industry and in the material of biotechnology industries. This material can be considered as a group of promising materials in the development of new health applications. The combination of phosphonic acid with LDHs material create a new hybrid material with new properties.In this work the synthesis of Zn/Al double lay-ered hydroxides by chemical co-precipitation method (molar ration 2) and grafted with Diamino Dodecyl Phosphonic Acid (DDPA) via anion-exchange mechanism. The samples were characterized and confirmed by X-ray diffraction (XRD), and the presence of diamino dodecyl phosphonic acid (DDPA ) was verified by Elemental analysis, BET analysis, and infrared spec-troscopy. Both of the samples were found to be showing antibacterial activ-ity. The zone diameters of Zn-Al- LDH were 40 mm and 25 mm for Esche-richia coli(ATCC 25922) and Streptococcus (ATCC 25922)and 20 mm for bacillus (ATCC 25922) whereas the same for hybrid LDH (Zn-Al-DDPA)were43 mm , 32 mm and 25 mm for the same bacteria showing stronger antibacterial activity of the grafted material over the material itself. The experimental results confirm the application of Zn-Al-DDPA in the field of antibacterial activities and may offer a promising antibacterial elucidation to the society.

Removal of sulfate from wastewater via synthetic Mg–Al layered double hydroxide: An adsorption, kinetics, and thermodynamic study

Sulfate-contaminated water is a major environmental problem that alters the taste of water, disturbs the digestive systems of animals and humans, and erodes both soil and metals. In this study, the layered double hydroxide LDH 4Mg2Al·NO3 and LDH 8Mg2Al·NO3 were prepared using a co-precipitation technique, and applied in the adsorption of SO42- from an aqueous solution. The reaction is well described by the Langmuir adsorption model. LDH 4Mg2Al·NO3 and LDH 8Mg2Al·NO3 afforded maximum SO42- adsorption values of 135.14 and 92.59 ​mg/g, respectively. The reaction is best explained by a pseudo-second-order mechanism, which suggests that chemisorption is the rate-determining step. The activation energies of LDH 4Mg2Al·NO3 and LDH 8Mg2Al·NO3 indicate that the adsorption of SO42- on synthetic LDHs predominantly follows an anion-exchange mechanism, wherein SO42- ions in the aqueous medium replaces intercalated NO3- ions in the synthetic LDHs. The thermodynamic parameters (ΔH̊, ΔS̊, and ΔG̊) were also calculated. The reaction was endothermic, and the synthetic LDHs afforded feasible and spontaneous adsorption of SO42-.

Extraction of gold(III) using novel gemini-type benzimidazole ionic liquid from hydrochloric acid medium

In this study, a novel gemini-type benzimidazole ionic liquid [C6BIM2][NTf2]2 was synthesized for efficient extract gold(III) from hydrochloric acid medium. Firstly, a series of parameters (e.g., vibrating time, the extractant concentration, acidity and salinity) were optimized and obtained the optimal extraction condition. Under this condition, the extraction efficiency can reach 98.42%, along with the distribution ratio of 186.87. Through the response surface methodology (RSM) model optimization, the amount of [C6BIM2][NTf2]2 corresponding to different HCl concentration was determined for gold(III) extraction during actual operation. Then, verified the anion exchange mechanism with the aid of Job’s method, UV–vis, FT-IR and 13C NMR. Thermodynamic parameters were calculated and implied that the extraction reaction was an exothermic and spontaneous process. Furthermore, organic phase loaded with gold(III) was easy to be completely stripped by CS(NH2)2/ HCl solution and its extraction ability was kept constant after 5 cycles extraction experiments. Meanwhile, [C6BIM2][NTf2]2 has a superb ability to select gold(III) in the multi-metal solution. In general, [C6BIM2][NTf2]2 showed distinguished selectivity and extraction ability for gold(III) from secondary resources, which was claimed to be a promising new style extractant.

A new method for highly efficient separation and determination of arsenic species in natural water using silica modified with polyamines

A simple and highly efficient method for the determination of highly toxic arsenic species using non-covalently aminated silica is proposed. The polyamines including poly(hexamethyleneguanidine), poly(4,9-dioxadodecane-1,12-guanidine), hexadimethrine, and poly(diallyldimethylammonium) were tested as silica modifiers. The prepared adsorbents allow effective preconcentration of anionic species of arsenic from aqueous solutions. It was found that As(V) can be quantitatively extracted from solutions at pH 4.5–7.0 by the anion exchange mechanism in less than 5 min, while neutral at this pH As(III) was not adsorbed at these conditions. A reaction with 2,3-dimercapto-1-propanesulphonic acid, which resulted in the formation of the negatively charged complex of As(III) with adsorbents was used for its quantitative extraction from solutions with a pH of 3.5–6.5. A system of two cartridges filled with poly(diallyldimethylammonium) modified silica and the on-line reaction of As(III) with 2,3-dimercapto-1-propanesulphonic acid proceeding between the cartridges was used for separate preconcentration and determination of As(V) and As(III) at pH 5. The proposed method was used for four-year monitoring of natural water pollution by arsenic in the area of residence of the indigenous peoples of Tyva Republic (Russia).

Tuning the extraction mechanism of uranyl ion in bicyclooctanium, propylpyridinium, piperidinium and imidazolium based ionic liquids: First ever evidence of 'cation exchange', 'anion exchange' and 'solvation' mechanism

A novel diamide ligand, 5-bromo-N1, N3-diisopropylisophthalamide has been synthesized and characterized by FTIR, 1H NMR, and 13C NMR. The extraction mechanism of uranyl ion with the diamide ligand has been studied in unexplored ionic liquid families. For the same metal–ligand system; cation exchange, anion exchange, and solvation mechanism can be predominately achieved by changing the ionic liquid system. The experimental results suggest that the change in extraction mechanism is induced by the cations of the ionic liquids. In bicyclooctanium ionic liquid, the extracted species was [UO2(NO3)3L2]-; In piperidinium and pyridinium-based ionic liquid, the species were UO2(NO3)2L and UO2(NO3)2L2 respectively. In imidazolium-based ionic liquid, the species was [UO2(NO3)L]+. Though the extraction efficiency in methylpyridinium and bicyclooctanium based ionic liquids are better, the pipiredinium and imidazolium-based ionic liquids exhibited a high degree of radiological stability. The aqueous solution of sodium carbonate is found to be better in the back extraction of uranyl ions from the ionic liquids relative to EDTA and oxalic acid. However, the efficacy of back extraction differs largely on the ionic liquid system.

Carbazole-based bis-ureas and thioureas as electroneutral anion transporters

ABSTRACT We report a series of easily accessible carbazole-based bis-ureas and thioureas as effective anion receptors and transporters. The compounds exhibit moderate Cl− binding affinity in wet DMSO and Cl− transport capabilities in phospholipid membranes predominantly through an electroneutral H+/Cl− and anion exchange mechanisms.

Homogenous Liquid–Liquid Extraction of Au(III) from Acidic Medium by Ionic Liquid Thermomorphic Systems

Two ionic liquid (IL) thermomorphic systems were designed. The thermoregulated property exhibited by the IL systems was utilized for the recovery of Au(III) from acidic medium. The cloud point order of the two ILs was proposed and evidenced via a combination of experimental measurements and quantum chemical calculations. The impacts of salt ions and acid on the thermomorphic phase behavior of the IL–H₂O binary mixture system were investigated. After comprehensive comparison, a systematic study of Au(III) extraction by the [Suc][Tf₂N]₂ (succinyl bis(trifluoromethylsulfonyl)imide) system was carried out because of its outstanding hydrophobicity and extraction ability. Then, a comparison between traditional liquid–liquid extraction (TLLE) and homogeneous liquid–liquid extraction (HLLE) was made during the process of optimization of various extraction parameters. In addition, the anion-exchange mechanism in the extraction process was revealed. The thermoregulated [Suc][Tf₂N]₂ system presented an excellent selectivity for Au(III) in a solution of coexisting multimetallic ions. Finally, Au(III) was almost completely stripped from the loaded IL phase by oxalic acid. The extraction efficiency of Au(III) using regenerated IL still maintains a surprising stability after five turns of cycling experiments. Hence, the dicationic IL [Suc][Tf₂N]₂ was regarded as a potential extractant for the recovery of gold.

Anion assisted extraction of U(VI) in alkylammonium ionic liquid: Experimental and DFT studies

The extraordinary extraction of metal ions in imidazolium ionic liquid phase containing neutral extractants was most often attributed to the cation exchange mechanism in addition to the usual solvation-type mechanism. The cation exchange mechanism results in an irreversible loss of the ionic liquid cation, which eventually leads to the pollution of aqueous phase also. To minimize the limitations of imidazolium based ionic liquid, strongly hydrophobic ionic liquids containing tetra-alkyl ammonium ion have been introduced and studied for actinide separation. Even though these tetra-alkyl ammonium ionic liquids did not undergo cation exchange, but showed exceptional extraction of actinides for the reason, which was not established so far. To unravel the unique role of these hydrophobic ionic liquids, the extraction behavior of U(VI) was studied in a solution of tri-n-octylmethylammonium nitrate ([N1888 ][NO3]) in conjunction with a neutral ligand, 2-hydroxy-N,N-dioctyl acetamide (DOHyA). The extraction of U(VI) was studied as a function of various extraction parameters and the organic phase obtained after extraction was probed by FTIR and Raman spectroscopy to elucidate the mechanism of U(VI) extraction in ionic liquid phase. The result revealed that U(VI) was extracted into ionic liquid phase by a couple of extraction modes, namely through metal–ligand coordination and by loss-less anion exchange mode and these pathways did not cause any undue burden to the organic and aqueous phases, unlike the traditional imidazolium ionic liquids. Further, DFT studies were performed to elucidate the underlying mechanism of U(VI) complexation in ionic liquid phase. The calculated values of binding energy (ΔE) and Gibbs free energy (ΔG) for the complexation of U(VI) with DOHyA in dodecane and tetra-alkyl ammonium ionic liquids medium were found in good agreement with the experimentally determined complexation trends of U(VI) ion with DoHyA. The DFT calculations further established that the cation exchange mechanism by both the ionic liquids, [N1888][NO3] and [N1888][NTf2] was not feasible, but anion exchange mechanism could be possible as observed in the experimental studies.

Amide-functionalised phosphonium-based ionic liquids as ligands for rhodium(iii) extraction.

Seven new amide-functionalised phosphonium-based ionic liquids (APILs) with chloride anions are synthesised and applied to extraction of rhodium(iii) from HCl solution. The effects of structural modification of the APILs on the extraction performance are examined by liquid–liquid extraction using toluene as a diluent and the results compared with those for trihexyltetradecylphosphonium chloride ([P66614][Cl]), a typical commercial extractant. The performance of the APILs as rhodium(iii) extractants is influenced by three main factors: (1) the length of the alkyl chains attached to the P atom; (2) the length of the linker between the amide and phosphonium moiety; and (3) the type of amide group. A novel ligand, [3°C2P444][Cl], had outstanding performance in the effective recovery of rhodium(iii). Extraction of rhodium(iii) from a 1.0 mol dm−3 HCl solution with 0.5 mol dm−3 [3°C2P444][Cl] proceeded quantitatively (>98%) and the extraction efficiency was higher than that of the commercial extractant [P66614][Cl]. The mechanism of rhodium(iii) extraction by [3°C2P444][Cl] was investigated by slope analysis, UV-vis, and FT-IR spectroscopy. These results indicate that [RhCl4(H2O)2]− in aqueous solution is extracted by [3°C2P444][Cl] through an anion-exchange mechanism and slowly converted into a dimer, [Rh2Cl9]3−, in the organic phase.

Synthesis of α-aminophosphonate based sorbents – Influence of inserted groups (carboxylic vs. amine) on uranyl sorption

A one-pot synthesis procedure is designed for preparing three α-aminophosphonates (R-H, R-COOH, and R-NH2); through the reaction of amine precursors (aniline, anthranilic or o-phenylene diamine, respectively) with salicylaldehyde and triphenylphosphite, under controlled conditions. These materials are first characterized by elemental analysis, FTIR, 1H NMR, 31P NMR, BET, DLS, pHzpc, TGA and titration. In a second step, the sorption properties are compared for U(VI) recovery from mildly acidic solutions. At the optimum pH (i.e., pH 4) the sorbents can be ranked according the series: R-H (1.057 mmol U g−1) > R-NH2 (0.746 mmol U g−1) > R-COOH (0.533 mmol U g−1). The isotherms are fitted by the Langmuir equation. Uranium uptake is relatively fast: under selected experimental conditions, the equilibrium is reached within 90 min of contact. The kinetic profiles are indistinctly fitted by the model of resistance to intraparticle diffusion and the pseudo-first order rate equation. The study of sorption thermodynamics shows substantial changes between the sorbents: uranyl uptake is endothermic with R-H and R-NH2 sorbents, while the reaction is exothermic with R-COOH sorbent. The diversity in functional groups and the speciation of uranyl in sulfuric acid solutions induce metal-binding through a combination of chelation and anion-exchange mechanisms (in function of pH). Sodium bicarbonate solutions achieve complete desorption of uranium from loaded-sorbents; the resins can be recycled for a minimum of 4–5 cycles with limited loss in efficiencies. The successful application of these resins for uranium recovery from acidic ore leachates demonstrates their promising properties for valorization of low-grade ores.

Different mechanisms of bicarbonate use affect carbon isotope composition in Ottelia guayangensis and Vallisneria denseserrulata in a karst stream

Abstract Macrophytes live in extremely different carbon environments compared to terrestrial plants. In response to bicarbonate dominated inorganic carbon in natural aquatic systems, the ability for HCO3− use has been developed in many macrophytes to alleviate a limitation by CO2 in aquatic systems. In the present study, all present macrophytes in a karst stream were investigated, and we found that seven of nine species were able to use HCO3− and two species at the source of the karst stream were restricted to CO2 use. Two different inhibitors were used to determine the HCO3− use mechanisms in Ottelia guanyangensis and Vallisneria denseserrulata, the only species coexisting from up- to down-stream. External carbonic anhydrase (CAext) mediated HCO3− use was present in O. guanyangensis up-stream, and then O. guanyangensis shifted to a combined mechanism of CAext and anion exchange (AE) mediated HCO3− use down-stream. In these two species, high HCO3− concentration induced the ability to use HCO3−, but high CO2 concentration inhibited this ability. From up-stream to down-stream, the decreasing CO2 induced increasing proportion of HCO3− use that led to changes in the δ13C in O. guanyangensis. However, a constant CAext and AE mediated HCO3− use caused a relatively stable δ13C in V. denseserrulata from river source to 330 m and then increased the proportion of HCO3− use at the stream outlet associated with the change in δ13C.