Subsequent Sulfonation Research Articles

Ammonia Adsorption Property of Fibrous PP-g-GMA-SO3H Adsorbent Prepared by Photoinduced Graft Polymerization and Subsequent Sulfonation

Ammonia Adsorption Property of Fibrous PP-g-GMA-SO3H Adsorbent Prepared by Photoinduced Graft Polymerization and Subsequent Sulfonation

Effect of acid soak treatment of the precursor on the structure and properties of polypropylene-based carbon fibers

Polyolefin fibers have received wide attention as the precursor for low-cost carbon fiber, and cross-linking of linear polyolefin by strong acid has been proven to be an effective way to stabilize the precursor fiber prior to carbonization. However, the conventional temperature used in sulfonation process is too high and could result in severe decomposition of the linear chain of the polymer, which further deteriorated the mechanical properties of the as-prepared carbon fiber. Thus, reducing the duration of sulfonation process operated at high temperature may alleviate the degradation behavior, conferring the polyolefin-based carbon fibers with better performance. In this paper, polypropylene (PP) fibers were soaked in sulfuric acid at 50 °C–90 °C, before the conventional preparation protocol of PP-based carbon fiber. The structural evolution from PP to carbon fiber were characterized by Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and Raman spectroscopy. The mechanical and conductive properties of carbonized fibers where further measured. The results showed that the soak in sulfuric acid resulted in swelling of PP fibers in diameter direction, as well as reducing the crystallinity of the fibers, both of which were physical transformation, and could be easily controlled by soak temperature. The subsequent sulfonation at conventional temperature was fastened for the soaked PP fibers, and the duration of sufficient sulfonation were almost reduced by half. The obtained carbon fibers exhibited better thermal conductivity and mechanical properties, which were enhanced by 25 % and 40 %, respectively, compared with that without soak pretreatment.

Designing Advanced Cross-Linked Proton Exchange Membranes with Enhanced Structural Homogeneity and Proton Conductivity via Radiation-Induced RAFT Polymerization.

This study introduces an innovative approach to fabricate well-defined cross-linked proton exchange membranes (PEMs) using radiation-induced reversible addition-fragmentation chain transfer (RAFT)-mediated polymerization on cost-effective ethylene tetrafluoroethylene (ETFE) films. The incorporation of the RAFT mechanism into the cross-linking process significantly enhanced structural homogeneity, providing uninterrupted proton conductivity. Thorough characterizations confirmed the successful grafting of polystyrene (PS) chains onto ETFE films and subsequent sulfonation. Despite a reduction in proton conductivity attributed to restricted chain movements, a notable improvement in chemical stability was observed after cross-linking reactions. Chemical stability of the cross-linked membranes increased approximately 4-fold compared to those synthesized without a cross-linker. The synthesized PEMs with degrees of grafting at 45% and 67% demonstrated superior proton conductivity, outperforming various alternatives, including commercial Nafion samples. Specifically, these cross-linked membranes exhibited promising proton conductivity values of 93.7 and 139.1 mS cm-1, respectively. This work highlights the potential of radiation-induced RAFT-mediated polymerization in carrying out cross-linking reactions as an efficient pathway for designing well-defined high-performance PEMs, offering enhanced homogeneity and conductivity compared to existing literature counterparts.

Catalytic Conversion of 5-Hydroxymethylfurfural and Fructose to 5-Ethoxymethylfurfural over Sulfonated Biochar Catalysts

5-Hydroxymethylfurfural (HMF) is a key platform compound that can be produced by the dehydration of typical carbohydrates like glucose and fructose. Among the derivatives of HMF, 5-ethoxymethylfurfural (EMF) is the etherification product of HMF with ethanol. Owing to some advantages (i.e., high energy density), EMF has been regarded as a potential liquid fuel. Therefore, catalytic conversion of HMF and fructose to EMF is of significance, especially using heterogeneous catalysts. In this paper, we demonstrated the preparation of biomass-based catalysts for the synthesis of EMF from HMF and fructose. Some sulfonated biochar catalysts were prepared by the carbonization of biomass-based precursors at high temperature in N2, followed by the subsequent sulfonation process employing concentered H2SO4 as sulfonation reagent. The obtained catalysts were characterized by scanning electron microscope (SEM), Fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD), and element analysis. The catalytic conversion of HMF to EMF was carried out in ethanol, providing a 78% yield with complete conversion at 120 °C. The catalytic activity of the used catalyst showed slight decrease for the etherification of HMF. Moreover, the catalysts were effective for the direct conversion of fructose towards EMF in 64.9% yield. Copyright © 2023 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Preparation of High-Performance Semihomogeneous Cation Exchange Membranes for Electrodialysis via Solvent-Free Polyethylene Particle-Confined Monomer Polymerization

The inherent two-phase structure of heterogeneous ion exchange membranes leads to defects in high area resistance and powder, which has greatly limited the application in electrodialysis. In this research, we have prepared a series of semihomogeneous cation exchange membranes from polyethylene-polystyrene (PE–PS) resin particles, which were synthesized via monomer absorption and PE particle-confined polymerization. The processing of semihomogeneous cation exchange membranes was conducted via thermoforming the PE–PS resin particles into films and subsequent sulfonation. The influence of the monomer content on water uptake, IEC, membrane area resistance, and electrodialysis performance was studied. The results proved that due to the excellent mechanical and film-forming characteristics of PE, the sulfonated membranes were still endowed with great mechanical properties, and the heating conditions enhanced the monomer absorption in polyethylene particles, which ensured high IEC for excellent electrodialysis performance after sulfonation. It was observed that the semihomogeneous cation exchange membrane (CEM-60) showed the highest NaCl desalination ratio (92.3%) and exhibited higher current efficiency (97.68%) and lowest surface area resistance (1.82 Ω·cm2), which exceeded the commercial cation exchange membrane CAM (6.96 Ω·cm2). These results suggested a promising future of semihomogeneous membranes.

Effects of source correction on positron annihilation lifetime spectroscopic analysis of graft-type polymer electrolyte membranes

Introduction: Recently, the free-volume hole features of poly(styrene sulfonic acid) (PSSA)-grafted poly(ethylene-co-tetrafluoroethylene) polymer electrolyte membranes (ETFE-PEMs) have been studied using positron annihilation lifetime spectroscopy (PALS) to determine the relationship between gas crossover through a PEM and a fuel cell. As one such series, this work investigates the source correction in PAL spectroscopic analysis for ETFE-PEM. Method: ETFE-PEM was prepared by radiation-induced graft polymerization and subsequent sulfonation. The free-volume hole characteristics of ETFE-PEM with a grafting degree (GD) of 106% were determined using PALS with and without source correction. Results: After source correction, the original-ETFE and ETFE-PEM strains exhibited increases in r3 (smaller radius of free-volume holes in the lamellar amorphous regions, the PSSA grafts, and the interface zones inside the lamellae) and r4 (larger radius of free-volume holes in the mobile amorphous layers and the PSSA grafts outside of the lamellae). In addition, the full width at half maximum (FWHM) of r3 is much greater than that of r4 due to the rearrangement in the mobile amorphous region and the polystyrene layers outside the lamellar structure. Conclusion: Source correction causes a significant change in the distribution curves of r3 for the original-ETFE and ETFE-PEM. Thus, source correction of positron annihilation lifetime spectroscopic analyses is an important issue for determining the o-Ps lifetime of polymers, which is near the lifetime of positrons in source materials.

Green acidic catalyst from cellulose extracted from sugarcane bagasse through pretreatment by electron beam irradiation and subsequent sulfonation for sugar production

The objective of this research is to prepare a green acidic catalyst from cellulose derived from sugarcane bagasse (SB). Initially, SB was pretreated by electron beam irradiation with a dose of 50 kGy to 200 kGy and subsequent acid hydrolysis to obtain cellulose. The cellulose derived from SB was carbonized at different temperatures for 4 h and then sulfonated with heating at 120°C under reflux. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were used to confirm the successful preparation of acidic catalyst by irradiation pretreatment and subsequent sulfonation. The cellulose derived from irradiated SB at the lowest dose of 50 kGy was used as a representative irradiated sample for comparison with non-irradiation. Scanning electron microscope image of sulfonated biochar was observed pores with various sizes. The existence of sulfur atom onto sulfonated biochar surface was investigated by Energy dispersive X-ray spectroscopy. After sugar production by sulfonated biochar as an acidic catalyst, the total sugar content was measured by a phenol-sulfuric acid method using a UV-Vis spectrophotometer. The total sugar with 94.51 ± 1.35% content was found when the acidic catalyst was performed. It was remarkable to note that sulfonated biochar prepared from cellulose derived from SB after pretreatment and sulfonation exhibited outstanding result for being as an acidic catalyst for sugar production.

Robust superhydrophobic coating fabricated on copper mesh with anti-corrosion property for oil/water separation

In this work, rod-shaped copper sulfide (CuS) nanostructures were synthesized on copper mesh (CM) by chemical oxidation and subsequent sulfonation. The obtained CuS nanostructures and further 1-dodecanethiol (DDT) modification endowed CM with extraordinary superhydrophobicity and self-cleaning ability. More importantly, the resulted CuS@DDT film was proved to improve the corrosion resistance of CM by electrochemical measurements in 3.5 wt% NaCl solution. Moreover, the fabricated mesh exhibited superior mechanical stability by adopting different mesh sandpaper for 20 abrasion cycles. Thus, the CuS@DDT CM with above exceptional performances was employed to successfully separate different types of oil from water and delivered desirable recyclability.

Renewable dissymmetric sulfonate gemini surfactants from addition of sodium hydrogensulfite to alkyl linoleate

AbstractA new series of bio‐based sulfonate gemini surfactants was synthesized through esterification of renewable linoleic acid with various alcohols and subsequent sulfonation with readily available sodium hydrogensulfite (NaHSO3). Organocatalytic sulfonation of methyl linoleate with NaHSO3 by the triethylamine and tert‐butyl peroxybenzoate catalyst system was investigated, where a methyl linoleate conversion of 96.4% could be achieved while generating high purity product without tedious purification. Three resulting sodium alkyl linoleate disulfonates (SALDs) have been characterized by Fourier transform infrared, high‐performance liquid chromatography, LC–MS, high‐resolution mass spectrometry (HR–MS), nuclear magnetic resonance techniques, and thermogravimetric analysis. The physicochemical properties and surface properties of the SALDs at various concentrations were investigated. The results showed that the SALDs exhibited low Krafft temperature, high water solubility, foam stability (foam half‐life time could reach 15 min), emulsifying ability (emulsification time of 2.0 g/L is 192 s), and good thermal stability. This study enriches the family of anionic gemini surfactants and provides reference data for facile preparation of gemini surfactants.

Lignin-Derived Ternary Polymeric Carbon as a Green Catalyst for Ethyl Levulinate Upgrading from Fructose

Currently, the utilization of lignocellulose mainly focuses on the conversion of polysaccharide components to value-added chemicals, such as ethyl levulinate (EL). Lignin is an important component of lignocellulosic biomass that is often neglected. Herein, ternary polymeric carbon (TPC–S) was synthesized by polymerization of mixed monomers (4-methylphenol, 4-ethylphenol, and 4-propylphenol) derived from lignin and subsequent sulfonation, which was used as a heterogeneous catalyst for the transformation of fructose to EL. Through a series of characterization methods, it was illustrated that the prepared catalyst had a layered porous structure. The calculated carbon layer spacing is 0.413 nm, and the average pore size is 5.1 nm. This structure greatly increases the specific surface area (165.2 m2/g) of the catalyst, which makes it possible to introduce more –SO3H species in the process of sulfonation, thus furnishing EL with increased yield. The effects of reaction temperature, time, catalyst dosage, and fructose initial concentration on the production of EL were investigated. It was found that 70.3% EL yield was detected at 130 °C for 10 h. In addition, the catalyst had good stability and could obtain 65.6% yield of EL in the fourth cycle. The obtained catalyst has the advantages of low cost, easy preparation, and high catalytic efficiency, which is expected to achieve efficient utilization of lignin and provide a potential solution for the future production of EL.

Synthesis of mesoporous sulfonated carbon from chicken bones to boost rapid conversion of 5-hydroxymethylfurfural and carbohydrates to 5-ethoxymethylfurfural

Sulfonated carbon material is an important class of catalysts, but controllable preparation of high-performance materials for biomass transformations is still challenging. Here, we demonstrate an effective strategy to prepare mesoporous sulfonated carbon materials from chicken bones to convert carbohydrates to 5-ethoxymethylfurfural (EMF). The carbonization of chicken bones without using additional templates gave hierarchical porous carbon materials. The subsequent sulfonation by chemical reduction approach introduced 2.33 mmol/g of -PhSO3H group, reserved abundant mesopores but blocked micropores. The sulfonated carbon materials afforded EMF yields of 94.7% and 68.6% from 5-hydroxymethylfurfural (HMF) and fructose in ethanol within 1.5 h and 2 h, respectively, without using high boiling point co-solvents. Furthermore, the apparent activation energies for HMF and fructose conversion were 29.1 and 49.5 kJ/mol, respectively. The catalyst could be reused four times with EMF yield decreasing from 68.6% to 62.7%.

Efficient conversion of glucose into 5-HMF catalyzed by lignin-derived mesoporous carbon solid acid in a biphasic system

A lignin-derived mesoporous carbon solid acid (LDMCS) catalyst was prepared by high temperature carbonization and subsequent sulfonation treatment using alkali lignin as the carbon source and KCl as a salt template. The prepared LDMCS has an irregular mesoporous structure with a narrow pore size distribution (concentrated at 4 nm), large specific surface area (1123.0 m2 g−1) and high -SO3H group density (2.20 mmol g−1). Compared with other types of solid acids reported in the literature, the prepared LDMCS catalyst has equivalent or better catalytic performance in the catalytic conversion of glucose to 5-hydroxymethylfurfural (5-HMF). A glucose conversion of 97.7% and a 5-HMF yield of 57.8% were obtained with the aqNaCl-THF (1:3) biphasic solvent system under the optimized reaction conditions with reaction temperature of 160 °C, reaction time of 2.5 h, and catalyst loading of 1 mg mg−1. More importantly, the 5-HMF yield still reached 40.9% after 5 cycles of the catalyst use, indicating that there was no significant loss of catalytic activity.

Renewable branched-chain sulfonate surfactants by addition of sodium hydrogensulfite to alkyl oleate

Branched-chain surfactants, with unique properties that make them amenable to exclusive applications, are currently typically synthesized from petrochemically derived Guerbet alcohols. Natural oleic acid, as one of the renewable platform molecules, is attracting increasing interest for the synthesis of surfactants due to its CC double bond and terminal hydrophilic carboxyl group. Herein, we report the synthesis of oleic acid-based branched-chain anionic surfactants with a sulfonate head group through terminal esterification of oleic acid with various alcohols (methanol, ethanol, and butanol) and subsequent sulfonation of the CC double bond using sodium hydrogensulfite. The three resulting alkyl oleate sulfonates have been characterized by FTIR, HPLC, LC-MS, HR-MS, and NMR techniques. Their surfactant properties, including equilibrium surface tension, dynamic surface tension, foaming property, and wetting ability, have been thoroughly investigated and compared with those of methyl ester sulfonate (MES), a linear chain analogue of alkyl oleate sulfonates. The results showed that the synthesized surfactants exhibited superior defoaming capacities (foam height after 1200 s is approximately 5% of initial foam height) and wettabilities (8 s, measured by the canvas descending method), in line with expectation for branched-chain surfactants, indicating their potential as primary surfactants for industrial cleaning products.

Mixed-acidic cation-exchange material for the separation of underivatized amino acids

Mixed-acidic cation-exchange (MCX) columns with both strongly (SCX) and weakly (WCX) acidic functional groups were developed for the separation of standard amino acids. The resins were prepared by carboxylation of highly crosslinked monodisperse poly(styrene-divinylbenzene) copolymer particles with performic acid and subsequent sulfonation with sulfuric acid. The degree of functionalization was varied independently for each processing step and controlled by measuring pH dependent retention of the obtained resins. A series of mixed-acidic resins with different SCX/WCX-ratios was chromatographically characterized by variation of formic acid and acetonitrile concentration in the aqueous eluent. The overall cation-exchange capacity was varied from 33 to 68 µmol/mL. The comparison with two commercial columns (Metrohm Metrosep C6, WCX and Hamilton PRP X-200, SCX) revealed the additive character of the different functional group properties within MCX columns and a unique selectivity which can be adjusted by both eluent composition and SCX/WCX-ratio of the resin. The retention window between neutral and basic amino acids was altered by varying the amount of sulfonic acid groups attached to the polymer. Orthogonality plots demonstrated constant selectivity for neutral amino acids. Correlating the retention data with log P data demonstrated the influence of non-ionic hydrophobic and π-π-interactions for the separation of amino acids on PS/DVB-based cation-exchangers. An isocratic IC-ESI-MS method was developed to separate and quantitate 20 underivatized standard amino acids within 30 min. Limits of detection were between 4 and 64 nmol L−1 and a high linearity of calibration curves was obtained for all analytes. The method was validated by comparing a certified reference standard with external calibration data.

Transformation of polyvinyl chloride (PVC) into a versatile and efficient adsorbent of Cu(II) cations and Cr(VI) anions through hydrothermal treatment and sulfonation

The reuse of waste polyvinyl chloride (PVC) has drawn much attention as it can reduce plastic waste and associated pollution, and provide valuable raw materials and products. In this study, sulfonated PVC-derived hydrochar (HS-PVC) was synthesized by two-stage hydrothermal treatment (HT) and sulfonation, and shown to be a versatile adsorbent. The removal of Cu(II) cations and Cr(VI) anions using HS-PVC reached 81.2 ± 1.6% and 60.3 ± 3.8%, respectively. The first stage of HT was crucial for the dichlorination of PVC and the formation of an aromatic structure. This stage guaranteed the introduction of -SO3H onto PVC-derived hydrochar through subsequent sulfonation. HT intensities (i.e., temperature and time) and sulfonation intensity strongly determined the adsorption capacity of HS-PVC. Competitive adsorption between Cu(II) and Cr(VI) onto HS-PVC was demonstrated by binary and preloading adsorption. The proposed Cu(II) cations adsorption mechanism was electrostatic adsorption, while Cr(VI) were possibly complexed by the phenolic -OH and reduced to Cr(III) cations by CC groups in HS-PVC. In addition, HS-PVC derived from PVC waste pipes performed better than PVC powder for Cu(II) and Cr(VI) removal (＞90%). This study provides an efficient method for recycling waste PVC and production of efficient adsorbents.

Improving the adhesion-to-fibers and film properties of corn starch by starch sulfo-itaconation for a better application in warp sizing

The purpose of this work was to develop a new starch-based sizing agent [sulfo-itaconylated starch (SIS)] with high adhesion and film properties, through starch sulfo-itaconation containing itaconation of acid-hydrolyzed starch (AHS) with itaconic anhydride and subsequent sulfonation with NaHSO3 in aqueous medium. The granular SIS was characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) techniques. The adhesion of SIS to cotton fibers was evaluated by a standard method (FZ/T 15001–2008). And its film properties were also investigated in terms of tensile strength, breaking elongation, moisture regain, bending endurance and degree of crystallinity, etc. The experimental results showed that the SIS samples had higher adhesion to cotton fibers and lower film brittleness than AHS as a control. Increasing the level of starch sulfo-itaconation could gradually enhance bonding strength to cotton fibers, and increase breaking elongation and bending endurance of SIS film, indicating that increasing the number of sulfo-itaconate substituents could play a significantly positive role in overcoming the shortcomings (insufficient adhesion and brittle film) of starch. Considering the previous results, the granular SIS with a modification level range of 0.034–0.041 showed potential for the use as a new starch-based sizing agent in paper-making and textile industry.

Hierarchical Porous Nitrogen-Doped Carbon Catalyst by the Pickering HIPE Technique: Synthesis and Application in HMF Production

In this paper, water-in-oil (W/O)-type Pickering high-internal phase emulsions (Pickering HIPEs) were stabilized using the modified SBA-15 with appropriate wettability as the stable particle. After thermal polymerization and subsequent sulfonation, we obtained hierarchical porous nitrogen-doped carbon catalysts (SNCs) with acid–base bifunctional active sites. The as-prepared catalysts have hierarchical porous structures, and acidic and basic catalytic activity centers, which can significantly improve the catalytic activity of the conversion of glucose to 5-hydroxymethylfurfural (HMF). The results showed that the highest HMF yield of 61.3% can be obtained, and the recovered catalyst still has a significant catalytic activity after four consecutive cycles. This work offers a versatile strategy for developing nitrogen-doped carbonaceous catalysts for a wide range of biomass transformation to platform chemicals.

Saccharification of cellulose using biomass-derived activated carbon-based solid acid catalysts

We prepared activated carbon-based solid acid catalysts derived from coconut shells via chemical activation with phosphoric acid under air and subsequent sulfonation. Their catalytic activities were evaluated in the saccharification of cellulose, and the parameters required for the activation and sulfonation processes were investigated. A catalyst activating temperature of 400 °C was found to be optimal, and the catalyst treated with chlorosulfuric acid exhibited a similar monosaccharide yield to that treated with fuming sulfuric acid. The prepared catalysts were characterized by various analytical techniques. The catalysts exhibited high specific surface areas and micropore volumes but low external specific surface areas. The catalysts had high contents of acidic functional groups when low activating temperatures were employed. For these catalysts, the surface chemical structure had a more dominant effect on the catalytic activity than that caused by the porous texture, while high acidic group contents led to high catalytic activities.

Process optimization of biodiesel production via esterification of oleic acid using sulfonated hierarchical mesoporous ZSM-5 as an efficient heterogeneous catalyst

The development of effective heterogeneous catalysts for the production of biodiesel from low-cost feedstocks containing large amounts of free fatty acids has lately become one of the foremost research issues in the energy research area. Herein, hierarchical mesoporous ZSM-5 zeolite containing sulfonic acid groups (SO3H-HM-ZSM-5-3) was prepared via the hard template approach, using soluble starch as a cheap and sustainable mesoporegen, and the subsequent sulfonation using chlorosulfonic acid as a sulfonating agent. The catalytic activity of the synthesized catalyst was evaluated in the esterification of oleic acid with methanol, and the principal process variables were optimized, adopting the response surface methodology. Results revealed that the catalyst amount and reaction temperature seemed to be the most influential variables governing the esterification process. A maximum oleic acid conversion of 100% was achieved under the optimum operating conditions of 18:1 methanol-to-oleic acid molar ratio and 5.2 wt% catalyst amount (based on the mass of oleic acid) at 88 °C, for 10 h. The performance of the developed SO3H-HM-ZSM-5-3 catalyst was comparable to or even outperformed some other reported acidic catalysts. Importantly, the performance of SO3H-HM-ZSM-5-3 for biodiesel production from waste cooking oil doped with 15% of oleic acid was additionally explored, and methyl ester yield as high as 92.45% was achieved through the simultaneous esterification of free fatty acids and the transesterification of triglycerides. Accordingly, SO3H-HM-ZSM-5-3 appears promising as an industrial catalyst for the one-step biodiesel production from low-grade feedstocks containing high levels of FFAs.

Surface features of polymer electrolyte membranes for fuel cell applications: An approach using S2p XPS analysis

Introduction: Hydrogen fuel cell is a promising renewable energy technology. Proton exchange membranes (PEMs) are an essential component of the fuel cell. Although the top surface nature of PEMs directly relates to the durability and efficiency of PEM fuel cells (PEMFC), there has been very limited attention on the chemical compositions and their distribution at the membrane surface. Thus, this study reports the surface characterization of poly(styrene sulfonic acid) (PSSA)-grafted poly(ethylene-co-tetrafluoroethylene) polymer electrolyte membranes (ETFE-PEMs) for fuel cell applications using S2p X-ray photoelectron spectroscopic (XPS) analysis. Methods: The ETFE-PEMs were prepared by radiation-induced grafting and subsequent sulfonation. The surface features of ETFE-PEMs with grafting degrees (GDs) of 55-101% were characterized using the survey-wide and narrow scans of S2p XPS. Results: The surface concentration of sulfur slightly decreased with increasing GDs. This interesting result has not been reported in the other graft-type PEMs. The four-component model of narrow scan deconvolution exhibited more reasonable results than the two-component model, in which the sulfonic acid groups (SO-3) slightly increased with increasing GD , not as the case observed by wide scan spectra due to the presence of by-products. Conclusion: The PSSA grafts were mainly generated inside the bulk rather than at the surface possibly due to the morphological changes. Moreover, the less presence of SO-3 group on the membrane surface despite the large GD values (GD = 55-101%) suggests the advanced electrolyte properties and interfacial stability for fuel cell applications.