Search

Interface modulation of nickel phosphide (Ni

With the drastic growth in the demand for lithium, recovery technologies that remove Li ions from a brine solution are attracting more interest. In this field, capacitive deionization (CDI) has bee...

Pseudocapacitive asymmetric supercapacitors are promising candidates for achieving high energy density in flexible energy storage devices. However, seeking suitable positive electrode materials that are compatible with negative electrode materials remains a considerable challenge. In the current study, a pseudocapacitive Ti3C2Tx MXene used as negative electrodes is rationally compatible with redox-type V2O5 as positive electrodes, resulting in the assembly of an all-pseudocapacitive Ti3C2Tx MXene//V2O5 asymmetric flexible energy storage device. The solid-state asymmetric device can deliver an energy density of 8.33 mW h cm-3 at a current density of 0.5 A g-1. Moreover, it can operate in an expanded voltage window of 1.5 V, with dominant surface-capacitive charge-storage mechanisms. Additionally, the device can power a yellow light-emitting diode for up to 7 s, indicating the potential of the device for use in practical applications. This study demonstrates the possibility of using other two-dimensional transition-metal carbide nanosheets for high-energy density flexible energy storage devices.

An electrochemical microchip sensor was fabricated through the photolithographic process. The metal paste used in the micro-pattern of the sensor chip contained dendritic and spherical Ag-coated Cu powders, which decreased the electrical resistance of the pattern down to 25.69 Ω·cm by forming a network for electron transfer between particles. The electrode materials were dendritic palladium oxide-nickel oxide powders that showed dramatically high surface area. Also, a synergetic effect on the sensing performance between palladium oxide and nickel oxide was observed. The formation of micro-pattern was investigated through optical microscope and field-emission scanning electron microscope. The body resistance of the conductive paste was calculated using the 4-point probe technique, and the electrochemical characteristics of the sensor were analyzed by cyclic voltammetry and chronoamperometry. The fabricated sensor chip exhibited sensing performance for hydrogen peroxide detection with high sensitivity of 641.75 µA mM−1 cm−2 in a dynamic range between 50 µM and 13 mM. Its long-term stability and high selectivity were also confirmed.

In this study, a quasi-solid-state supercapacitor with high energy density was successfully developed using a zwitterionic gel electrolyte with a dual-function redox additive. A polyzwitterion charged polymer, poly([2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide) (PPDE), was used with LiCl as the flexible gel electrolyte. This proposed electrolyte demonstrates promise for use in practical supercapacitors due to its environmental friendliness, transparency, flexibility, and high ionic conductivity. To further improve the electrochemical performance, a dual-function redox additive, ethyl viologen dibromide, was incorporated into the polyzwitterion. With the redox mediator in the polyzwitterionic electrolyte (PPDE-LiCl-EV), the specific capacitance improved by a factor of three compared to the pristine zwitterionic polymer (178 F g−1 for PPDE-LiCl and 677 F g−1 for PPDE-LiCl-EV) due to additional faradaic reactions. In addition, a quasi-solid-state supercapacitor incorporating PPDE-LiCl-EV exhibited a high energy density of 542 Wh kg−1 and a power density of 2.88 kW kg−1 over a wide potential window of 2.4 V. Fourier transform infrared spectroscopy in attenuated total reflectance mode was employed for in situ monitoring of the redox reactions of additives on the electrode surface. To the best of our knowledge, this is the first attempt to analyze the redox reactions of redox additives.

We synthesized a novel quaternized anion exchange membrane (AEM) that exhibits high ionic conductivity and structural stability, even under high pH conditions, by copolymerizing a chitosan-based membrane with vinylimidazole derivatives. During the process, a quaternized poly[O-(2-imidazolyethylene)-N-picolylchitosan (QPIENPC) was synthesized by modifying chitosan with a 4-pyridinecarboxaldehyde derivative and then copolymerizing the modified chitosan with 1-vinylimidzaole. The results revealed that the degree of quaternization is correlated with ionic exchange capacity, water absorption ability, linear expansion ratio, and hydroxide conductivity of the resulting membrane. The QPIENPC membrane was characterized by a high ionic conductivity of 10.15 mS cm−1, 14 times greater that of the unfunctionalized chitosan membrane, as well as by low water absorption ability (36.17%) and linear expansion ratio (20.49%) at 80 °C. An alkaline direct methanol fuel cell (ADMFC) was fabricated using the prepared QPIENPC membrane as an anion exchange electrolyte membrane, with PtRu/C and Pt/C as the anode and cathode, respectively. The performance of this ADMFC is promising even under high pH conditions, with the peak power density of 10.42 mW cm−2 and corresponding current density of 28.76 mA cm−2. Moreover, the thermochemical and mechanical strengths of the QPIENPC membrane were higher than those of the chitosan membrane.

Solid polymer electrolytes (SPEs) for Li-metal polymer batteries are prepared, in which poly(ethylene oxide) (PEO), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), and copper-oxide fillers are formulated. Their structural and electrochemical properties are analyzed when the morphology of the copper-oxide fillers has been modulated to spherical or dendritic structure. The ionic conductivity obtained by electrochemical impedance spectroscopy (EIS) has been increased to 1.007 × 10−4 S cm−1 at 30 °C and 1.368 × 10−3 S cm−1 at 60 °C, as the 5 wt% dendritic fillers have been added to the SPEs. This ionic conductivity value is 1.3 times higher than that of 5 wt% spherical filler-contained SPEs. The analyses of differential scanning calorimetry (DSC) and X-ray diffraction (XRD) indicate that the increase of ionic conductivity is due to the remarkable decrease of crystallinity upon the addition of copper-oxide filler into PEO matrix of SPEs. The fabricated SPEs with the dendritic copper-oxide fillers present a total ionic transference number of 0.99 and a lithium-ion transference number of 0.38. More importantly, it presents a stable potential window of 2.0–4.8 V at 25 °C and high thermal stability up to 300 °C. The specific discharge capacity of the prepared cell with the dendritic filler-contained SPEs is measured to be 51 mA h g−1 and 125 mA h g−1 under 0.1 current-rate (C-rate) at 25 °C and 60 °C, respectively. In this study, the ionic conductivity and the electrochemical performance of the PEO-based polymer electrolyte have been evaluated when morphologically different copper-oxide fillers have been incorporated into the PEO matrix. We have also confirmed the safety and the flexibility of the prepared solid polymer electrolytes when they are used in flexible lithium-metal polymer batteries (LMPBs).

Pseudocapacitive asymmetric supercapacitors are promising candidates for achieving high energy density in flexible energy storage devices. However, seeking suitable positive electrode materials that are compatible with negative electrode materials remains a considerable challenge. In the current study, a pseudocapacitive Ti

v Photocatalytic CO2 reduction is a technology which converts carbon dioxide into high value-added chemicals, simultaneously resulting in a reduction of carbon dioxide and the production of useful chemicals. To increase the conversion efficiency and product selectivity, various parameters such as the light absorption efficiency, catalytic reaction activity on the electrode surface, and charge separation efficiency must be considered. In this study, photocatalytic CO2 reduction was investigated using an inorganic halide perovskite-based photocatalyst with a copper scaffold as a co-catalyst. We found that, when the two catalyst materials are used together, the photosensitized perovskite-based photocatalyst efficiently delivers excited electrons to the copper scaffold and produces a higher variety of products (for example, CH4, C2H4, and C2H6) than that without the copper scaffold. During photo-irradiation, a multi-scattering process occurs in the copper scaffold, which generates more photo-induced carriers, resulting in an enhanced light harvesting ability compared to that of the planar structure without the porous scaffold. Therefore, the CsPbBr3 perovskite catalysts embedded in a porous copper scaffold exhibit superior photocatalytic performance toward CO2 reduction. In the photocatalytic reduction reaction of CO2 on the perovskite photocatalyst with a copper scaffold, ethylene (C2H4, 46.5 μmol/g) was a major product and methane (CH4, 18.9 μmol/g), ethane (C2H6, 17.1 μmol/g), and propane (C3H8, 11.3 μmol/g) were additionally detected. On the other hand, the planar perovskite photocatalyst has very low catalytic activity for CO2 reduction and only methane (CH4, 17.2 μmol/g) was observed as a main conversion product from CO2 after light irradiation. Additionally, in this work, in-situ ATR-IR analysis was performed to understand the photocatalytic CO2 reduction mechanism.

Asymmetric supercapacitors with positive electrodes based on transition metal sulfides show high specific capacitance with higher energy density than that of carbon-based supercapacitors, which suf...

Functional groups in two-dimensional (2D) Ti3 C2 Tx MXene are an important factor influencing electrochemical performance in many applications involving energy storage, electrochemical sensors, and water purification. However, after dimethyl sulfoxide (DMSO) delamination, the effect of surface functionalities in Ti3 C2 Tx is still unclear and there are no systematic reports on its capacitive behavior. Experiments and theoretical calculations confirm the relationship between different surface functionalities, the DMSO delamination effect, and the electrochemical behavior of the DMSO-delaminated Ti3 C2 Tx . The dominant -O and -OH terminations are attributed for surfaces delaminated by using HF [Ti3 C2 Tx (HF)] and LiF/HCl [Ti3 C2 Tx (LiF/HCl)], respectively. Theoretical results are also in agreement with experimental results in that -OH terminations are essential for the formation of a free-standing film. Compared to non-delaminated Ti3 C2 Tx (HF) (similar O/F ratios of 1.37 and 1.42), there is a significant DMSO delamination effect for Ti3 C2 Tx (LiF/HCl) because of different O/F ratios of 2.9 and 3.6. Additionally, the delaminated Ti3 C2 Tx (LiF/HCl) electrodes deliver a higher capacitance of 508 F cm-3 than that of 333 F cm-3 for the delaminated Ti3 C2 Tx (HF), although it exhibited lower equivalent series resistance, lower interlayer spacing, and slightly lower specific surface area. This study provides direct and systematic experimental evidence for different functional groups in Ti3 C2 Tx MXene based on the DMSO delamination effect.

Free-standing Ti3C2Tx MXene films with flexible feature are considered to be promising electrodes for the application in flexible energy devices. Exploring the different cation effect and each transport mechanism will help us to identify the optimized cation for special applications. Herein, we investigate the relationship between cation transports and capacitance behavior under different potential windows. In addition, we uncover intercalation mechanisms for Li+, Na+, and K+-containing electrolytes. As a result, we found that capacitive intercalation mechanism of characteristic cation can be influenced by different potential windows. Importantly, after 5000 charge-discharge cycles from −1 V to 0 V, the cation-intercalation behavior is demonstrated by significant electrode expansion in LiCl, NaCl, and KCl electrolytes with the increased d-spacing of 1.344 nm, 1.313 nm, and 1.305 nm, respectively. Additionally, larger size of K+ with fast ion transport is involved in fast electrochemical surface adsorptions, which explains higher capacitance of 346 F cm−3 in KCl than 218 F cm−3 in NaCl electrolyte. In contrast, small ion size of Li+ is vulnerable to adsorb and permeate the spacing between layers of Ti3C2Tx MXene electrode, which delivers volumetric capacitance of 320 F cm−3. The present study provides direct experimental evidence for electrochemical mechanism of cation intercalation between Ti3C2Tx MXene layer sheets.

The capacitive deionization (CDI) is a potential desalination technology in which brackish water flows between electrodes; by this process, ions are generated and stored in an electrical double layer formed at the electrode surface. In this work, we report efficient electrode materials which enable the capacitive deionization system to overcome the several issues of desalination. The rGO–SnO2 nano-composite has been fabricated by an eco-friendly and facile hydrothermal process. The synthesized composite presents an improvement in electrochemical performance and an excellent capacitance retention of 60% even at relatively high scan-rates. In a specially designed CDI cell, the synthesized nanocomposite has shown excellent cyclic performance, high reversibility, and a remarkable electrosorption capacity of 17.62 mg g−1 at an applied potential of 1.2 V with an initial salt concentration of 400 mg L−1. The enhancement in electrosorption capacity of the electrode emerges due to its high specific capacitance in NaCl aqueous solution. Moreover, the system has shown a fast ion-removal rate with excellent stability and reversibility in an aqueous sodium-chloride (NaCl) solution. These results suggest that the rGO–SnO2 composite prepared in this work is a feasible electrode material for desalination in the capacitive deionization process.

Effects of the crystalline tungsten carbide (WxC) phases on an ordered mesoporous bimetallic Rh-Mn/WxC, which were prepared by changing carbon source to tungsten (C/W) ratios of the WxC support using a hard-template of an ordered mesoporous SBA-15, were investigated for a direct synthesis of mixed alcohols by CO hydrogenation from syngas. The C/W ratios on the mesoporous Rh-Mn/WxC showed a significantly different catalytic activity, especially on the C 1 - C 3 alcohol productivity. The Rh-Mn/WxC prepared at C/W molar ratio of 10 having a metastable W 2 C main phase (Rh-Mn/WxC(10)) revealed a higher CO conversion of 8.1% and selectivity to higher alcohols of 54.4% compared to other catalysts having a main crystalline phases of WO 3 or WC. The enhanced catalytic activity and selectivity to mixed alcohols on the Rh-Mn/WxC(10) were attributed to the largely exposed smaller active Rh nanoparticles with its stronger interactions with the metastable W 2 C phases. The superior activity was originated from the intimate interactions of Rh nanoparticles with Mn promoter by maintaining proper oxidation states confirmed by surface ratios of the metallic Rh to oxidized Rh n+ species. The stable preservation of the ordered mesoporous structures of the W 2 C phase in the amorphous carbon matrixes significantly altered the chemical states of the small Rh nanoparticles below 2 nm in size by preferentially existing on the outer surfaces of the W 2 C support, which resulted in showing an enhanced productivity of higher C 1 –C 3 alcohols with 171.8 g/(kg cat ·h).

Highly accurate and prompt monitoring of cortisol is imperative for the prevention of stress-related diseases. In this study, we present a novel electrochemical biosensor for cortisol detection harnessing an electrochemical sensing platform consisting of a reduced graphene oxide (rGO) electrode, a bifunctional protein interlayer, and an antibody probe that specifically recognizes cortisol molecules. A thermally denatured bovine serum albumin (d-BSA) protein layer was directly adsorbed as an interlayer onto the rGO electrode surface via pi-stacking interactions, which provides the bifunctionality of creating covalent anchoring sites for anti-cortisol antibody probes and preventing the nonspecific binding of undefined substances. Electrochemical impedance spectroscopic (EIS) measurements show that the constructed sensing platform (antibody/d-BSA/rGO) exhibits picomolar-range sensitivity cortisol detection with a wide linear dynamic range spanning 10 pM–100 nM. In addition, our sensor exhibits high selectivity toward cortisol with negligible cross-binding reactivity to the cortisol analogs, aldosterone and progesterone. Moreover, almost complete spike recovery was confirmed with cortisol present in human saliva samples containing several interfering compounds. The demonstrated strategy for constructing the protein/rGO composite sensing platform is simple but versatile. Therefore, it is expected to facilitate efficient interfacing of various biomolecular probes with graphene-based and/or other electrode materials with hydrophobic surfaces.

Dendritic copper powders are highly desirable in many applications, including electromagnetic interference shielding and conductive pastes, because of low cost and high conductivity. We prepared dendritic copper powders using the galvanic displacement reaction between the Al and Cu-ions in aqueous solution. This method is very simple and spontaneous at room temperature. During the process, the morphology of the copper powders is strongly affected by several variables, such as the displacement reaction rate and the amount of hydrogen evolution due to the reduction of proton. The effect of the different composition of electrolytes to morphological changes of copper powders was investigated in this study. In addition, the effects of concentration of chlorine ion, pH, termination time, and additives were monitored, which resulted in different morphology. Considering different applications, such as sensors, catalysts, and conductive pastes, the controllability of the morphology of dendritic copper powders plays an important role in achieving high performance in desired applications.

A simple electrochemical method is reported for the preparation of Ni2FeS4 (NFS) nanosheets on carbon sheet (CS)substrate. FESEM and EDAX data confirmed the presence of nanosheet morphology with required stoichiometry. NFS modified CS is employed as an electrode material for the development of non-enzymatic glucose sensor. Impedance data showed low charge transfer resistance for NFS/CS compared to bare CS, indicated its high charge transfer capability. The developed sensor exhibited wide linear response in two different glucose concentration ranges of 10 to 1850 μM and 2350 to 7750 μM with the sensitivity value of 0.71 μA μM−1 cm−2 and 0.14 μA μM−1 cm−2. Moreover, the selectivity data demonstrated good anti-interference property of NFS/CS towards glucose in the presence of possible interfering species viz. ascorbic acid, dopamine and uric acid.

Direct activation of CH4 to oxygenates and unsaturated light hydrocarbons was investigated using Fe-modified ZSM-5 and Ferrierite (FER) for a partial oxidation of CH4 with N2O oxidant. The amount of active α-oxygen sites and number of Bronsted acid sites on the Fe-modified zeolites were well correlated with CH4 conversion rate and product distributions. The amount of α-oxygen sites was largely changed according to preparation method such as wet impregnation or ion-exchange of iron precursor and types of zeolites. A large number of Bronsted acid sites and α-oxygen sites on the Fe-modified FER revealed a higher oxygenate formation such as methanol and dimethyl ether (DME) with COx, and a larger number of strong acid sites on Fe-modified ZSM-5 was also responsible for a higher selectivity to light hydrocarbons by a successive dehydration of oxygenates formed. The different catalytic performances were verified through proper measurements of the amount and type of acidic sites as well as the α-oxygen sites measured by N2O pulse chemisorption. The Fe-modified FER prepared by impregnation method possessed a larger amount of α-oxygen sites due to abundant Bronsted acid sites, which was responsible for a higher rate of CH4 conversion to oxygenates with the help of N2O decomposition on the α-oxygen sites originated from iron oxide nanoparticles.

SnO2 is a well-studied anode material for lithium ion batteries (LIBs). However, it undergoes severe capacity fading because of a large volume change (∼300%) during cycling. Composites of SnO2 with electro-conductive graphene would deliver improved capacity and rate performance. Nevertheless, achieving the theoretical capacity of SnO2 is still elusive, mainly because of disintegration of the active material from graphene and severe aggregation of SnO2, or Sn nanoparticles produced upon cycling. To surmount these limitations, in this work, nanocomposites containing ultra-fine sized SnO2 nanoparticles (UFSN) with reduced graphene oxide and amorphous carbon were synthesized in a single step at low temperature and environmentally benign way, in which ascorbic acid was employed as the carbon source and reducing agent. UFSN could decrease the lithium ion diffusion path length. As a result of effective buffering effect afforded by the mesoporous structure against volume change and improved lithium ion diffusivity, the ternary nanocomposite achieves ultra-high capacity of 1245 mAh g−1 after 210 cycles at 100 mA g−1 and excellent cycling stability. Since the proposed approach is facile, straightforward, and highly reproducible, it is anticipated that this system would be a potential alternative to the conventional graphite anode for LIBs.

Self-doped semiconductors have recently attracted extensive interest as highly efficient photocatalytic materials because the electronic properties can be modulated without sacrificing the chemical stability of the parent material. In this report, we report the facile synthesis of Sn2+ self-doped SnS microparticles via a simple template-free hydrothermal route. Because of the ability to successfully tune the band structure while minimizing defect generation, self-doped SnS could potentially serve as an efficient photocatalyst of wastewater. Here, Sn2+ self-doping results in insertion of an energy level slightly below the conduction band of SnS, thereby decreasing the photoexcitation energy. Furthermore, dopant sites can act as charge trapping sites, which can consequently minimize problematic charge recombination. Synthesized materials were characterized by various spectroscopic, microscopic, and surface characterization techniques, all of which confirmed the formation of self-doped SnS. The Sn2+ self-doped SnS photocatalyst successfully reduced carcinogenic Cr(VI) to the water-insoluble Cr(III) form under visible light illumination. The best photocatalytic efficiency was obtained from an optimal balance between increased numbers of trapping sites leading to longer charge carrier lifetime, and decreased distance between trapping sites, favoring charge recombination. We anticipate that similar methodologies can be applied to other non-stoichiometric semiconducting photocatalysts with tunable electronic properties and enhanced photocatalytic efficiency.

Gel electrolytes are considered to be promising candidates for the use in supercapacitors. It is worthy to systematically evaluate the internal electrochemical mechanisms with a variety of cations (poly(vinyl alcohol) (PVA)-based Li+, Na+, and K+) toward redox-type electrode. Herein, we describe a quasi-solid-state PVA-KCl gel electrolyte for V2O5·0.5H2O-based redox-type capacitors, effectively avoiding electrochemical oxidation and structural breakdown of layered V2O5·0.5H2O during 10 000 charge–discharge cycles (98% capacitance retention at 400 mV s–1). With the gel electrolyte, symmetric V2O5·0.5H2O-reduced graphene oxide (V2O5·0.5H2O-rGO) devices exhibited a volumetric capacitance of 136 mF cm–3, which was much higher than that of 68 mF cm–3 for PVA-NaCl and 45 mF cm–3 for PVA-LiCl. Additionally, hybrid full cells of activated carbon cloth//V2O5·0.5H2O-rGO delivered an energy density of 102 μWh cm–3 and a power density of 73.38 mW cm–3 over a wide potential window of 2 V. The present study provides di...

Two steps of wet chemical processes have been developed for the preparation of core-shell nanostructures of copper and silver, which is a facile and low cost method for the production of large quantity of dendritic powders. First step involves a galvanic displacement reaction with hydrogen evolution which is the motive force of spontaneous electrochemical reaction. To achieve the core-shell structure, silver has been coated on the dendritic copper using the galvanic displacement reaction. The dendritic silver-coated copper powders exhibit high surface-area, excellent conductivity, and good oxidation resistance. It has been found that silver-coated copper powders maintain the electrical conductivity even after annealing at 150 °C for several to tens of minutes, thus it is a promising material and an alternative to pure silver powders in printed electronics application.

The oriented synthesis of high-performance nanobelt/graphene hybrids remains a challenge by one-step environmentally friendly process for supercapacitors. Here, PEG-6000 manipulation was employed to facilitate ultra-long V 2 O 5 ·0.5H 2 O nanobelts on surface of reduced graphene oxide (rGO). As a result, due to faster and efficient electron transfer and collection, V 2 O 5 ·0.5H 2 O/rGO hybrid (rGO: 5 wt%–50 wt%) significantly enhances electrochemical capacitance for supercapacitors. Especially, introduction of 50 wt% rGO in the hybrid (denoted as 50 wt% rGO-V) exhibits a high capacitance of 649 F g −1 at a scan rate of 5 mV s −1 in a neutral KCl electrolyte. On the other hand, the hybrid material shows a high-rate capacitance of 160 F g −1 at a current density of 1 A g −1 . Additionally, capacitance retention of 93% was obtained after 600 cycles, implying excellent cycling stability in the 50 wt% rGO-V hybrid. This study is beneficial to understand synergetic effects in V 2 O 5 ·0.5H 2 O/rGO hybrid materials and even useful for oriented synthesis of hybrid materials in other energy storage devices.

CO hydrogenation to hydrocarbons through Fischer–Tropsch synthesis (FTS) reaction is one of the promising chemical processes, which can convert alternative feedstocks such as natural gas or biomass into synthetic fuels. The FTS reaction has received many attentions due to a limited petroleum resource with an increased demand for using alternative carbon sources such as stranded gas or shale gas. Some proper synthetic methods of an effective FTS catalyst having a larger active metal surface area and a lower deactivation rate are the most important issues for a long-term operation. Therefore, some ordered mesoporous materials (OMM) have been widely investigated in the field of CO hydrogenation using some heterogeneous catalysts. The present brief review paper summarized the various preparation methods of the ordered mesoporous materials for the possible applications of FTS reaction with a lower deactivation rate and a higher catalytic performance. The applications of the ordered mesoporous cobalt oxides for FTS reaction are briefly introduced and the ways to improve a structural stability even under reductive CO hydrogenation conditions by using efficient pillaring materials as well as by preparing mixed metal oxides. A higher catalytic activity of the ordered mesoporous cobalt oxide was also verified in a multi-channel fixed-bed compact reactor having the intersected interlayers of micro-channel heat exchanger. The thermal stability of ordered mesoporous cobalt-based catalysts was mainly affected by a structural stability which can easily remove the heavy hydrocarbons from the inner surfaces.

The amounts of Bronsted acid sites on K, P, and Zr-modified microporous Ferrierite zeolite were investigated through pyridine FT-IR and NH3-TPD analyses. P-modified Ferrierite showed a superior catalytic activity for methyl acetate synthesis by esterification of methanol and acetic acid. The catalytic activity at steady-state with the acidic properties of as-prepared catalysts was well correlated with the results of pyridine FT-IR (intensity ratio of Bronsted acid sites to total acid sites) compared with that of NH3-TPD. The results can suggest the proper and simple method to estimate the esterification activity at steady-state using the measured acid sites on the as-prepared zeolites.