Korean Journal of Chemical Engineering (v.36, #2)

The exceptional quality of light generated from colloidal quantum dots has attracted continued interest from the display and lighting industry, leading to the development of commercial quantum dot displays based on the photoluminescence down-conversion process. Beyond this technical level, quantum dots are being introduced as emissive materials in electroluminescence devices (or quantum dot-based light-emitting diodes), which boast high internal quantum efficiency of up to 100%, energy efficiency, thinness, and flexibility. In this review, we revisit various milestone studies regarding the core/shell heterostructures of colloidal quantum dots from the viewpoint of electroluminescence materials. Development of nanostructured colloidal quantum dots advanced from core/shell heterostructure, core/thick shell formulation, and delicate control of confinement potential shape has demonstrated close correlation of the photophysical properties of quantum dots with the performance of electroluminescence device, which provided useful guidelines on the heterostructured quantum dots for mitigating or eliminating efficiency limiting phenomena in quantum dot light emitting diodes. To enable practical and high performance quantum dot-based electroluminescence devices in the future, integration of design concepts on the heterostructures with environmentally benign systems will be crucial.
Keywords: Colloidal Quantum Dots; Nanocrystals; Core/Shell Heterostructures; Electroluminescence; Light Emitting Diodes

As the popularity of coffee beverage increases, an upsurge in the amount of solid residue, known as spent coffee ground (SCG), is inevitable. Currently, SCG is disposed of in the form of solid waste. However, there is a considerable amount of some valuable compounds including phenolic compounds in SCG. In this work, SCG was adopted as a natural antioxidant source for recovering phenolic compounds by an extraction method. An aqueous ethanol solvent (30% v/v) was used at different conditions of temperature, extraction time, and liquid/solid ratio. The amounts of phenolic compounds were analyzed by the well-known Folin-Ciocalteu method, and values were expressed as the weight of gallic acid equivalent (GAE). The highest extraction yield (87.3%) was reported at the highs of process variables; temperature=60 °C, extraction time=150 min, and liquid/solid ratio= 50 mL/g, based on a full factorial experimental design. The statistical Student’s t-test applied to the three operating factors revealed that temperature and liquid/solid ratio are more significant than the extraction time. A correlation equation was proposed to quantitatively analyze the effect of the factors on the reduction yield which could be further used to design and optimize the extraction process.
Keywords: Spent Coffee Ground; Phenolic Recover; Extraction; Aqueous Ethanol; Waste Reduction

Effects of Al3+ precipitation onto primitive amorphous Cu-Zn precipitate on methanol synthesis over Cu/ZnO/Al2O3 catalyst by Cheonwoo Jeong; Jongha Park; Jinsung Kim; Joon Hyun Baik; Young-Woong Suh (191-196).
The phase of Cu,Zn,Al precursors strongly affects the activity of their final catalysts. Herein, the Cu,Zn,Al precursor was prepared by precipitation of Al3+ onto primitive, amorphous Cu,Zn precipitate. This precursor turned out to be a phase mixture of zincian malachite and hydrotalcite in which the latter phase was less abundant compared to the co-precipitated precursor. The final catalyst derived from this precursor exhibited a little higher copper surface area and methanol synthesis activity than the co-precipitated counterpart. Therefore, the two precursor phases need to be mixed in an adequate proportion for the preparation of active Cu/ZnO/Al2O3 catalyst.
Keywords: Methanol Synthesis; Cu/ZnO/Al2O3 ; Sequential Precipitation; Precursor Phase

Although the production of cyclic carbonates from CO2 and epoxides can be promoted by eco-friendly halogen- and metal-free organic catalysts, its homogeneity complicates the catalyst reuse. Herein, we synthesized solid multifunctional alkanolamines using simple epoxy and amine reactions, and analyzed their structures by IR and 13C-NMR. Then, we employed these as catalysts for CO2 cycloaddition with propylene oxide, obtaining propylene carbonate in 98% yield after 3 h at 120 °C. Moreover, at 60 °C, the reaction was successfully repeated five times and a product yield of 50% was maintained throughout.
Keywords: Alkanolamine; Carbon Dioxide Fixation; Metal- and Halide-free; Solid Catalyst; Propylene Carbonate

Lactide, a six-membered dimeric cyclic ester of lactic acid, is a key building block of polylatic acid, a representative bio-based biodegradable polymer. As an alternative to the conventional lactide production process of a two-step polymerization and depolymerization from lactic acid, we developed a novel continuous and one-step synthesis of optically pure lactide from lactic acid under atmospheric conditions with SnO2-SiO2 nanocomposites as heterogeneous catalyst. In this catalytic process, lactide was obtained in vapor phase together with water vapor and the unreacted lactic acid. After optimization of crystallization process using ethanol solvent, lactide crystals with 99 wt% purity and a lactide yield of 78 wt% were obtained. Based on these results, an integrated process for high-yield polymer-grade lactide production from aqueous lactic acid could be constructed by combination of the heterogeneous catalysis and crystallization with ethanol, which is more environmentally friendly as compared to the conventional two-step prepolymer process.
Keywords: Lactic Acid; Lactide; Catalysis; Crystallization; Ethanol

Hierarchical ZSM-5 zeolites with different SiO2/Al2O3 ratio but similar crystal size were directly synthesized by a single-template hydrothermal method, and the intrinsic effect of acidic properties on their catalytic performance in methanol to gasoline (MTG) reaction was comprehensively investigated. The physicochemical properties of HZSM-5 zeolites were characterized by XRD, N2 adsorption-desorption, SEM, NH3-TPD, FTIR, and TGA techniques. The results show good linear correlations between the yields of gasoline components and the relative content of Brønsted acid sites, and the hierarchical HZSM-5 zeolite with SiO2/Al2O3 molar ratio of 200 was firstly found to exhibit high reactivity, excellent product distribution and superior stability in MTG reaction, which can be attributed to its appropriate acid distribution with moderate Brønsted acid sites and proper B/L ratio, predominantly promoting gasoline range hydrocarbons production and inhibiting side reactions.
Keywords: Methanol; Gasoline; Hierarchical HZSM-5 Zeolites; Acidity; Deactivation

Degradation and removal of p-nitroaniline from aqueous solutions using a novel semi-fluid Fe/charcoal micro-electrolysis reactor by Mohammad Malakootian; Mostafa Pournamdari; Ali Asadipour; Hakimeh Mahdizadeh (217-225).
p-Nitroaniline (PNA) is a common contaminant in the wastewater of oil refineries, the petrochemical industry and from production of pesticides, dyes and glue. The aim of this research was to determine the extent of degradation and removal of PNA from aqueous solutions by a novel semi-fluid Fe/charcoal reactor, process optimization, determination of the intermediate and final products and the degradation reaction path. The effective factors in the degradation process were contact time, aeration amount, initial PNA concentration, Fe/charcoal ratio, and initial pH of the solution. The intermediate products were determined by GC-MS. The kinetics of the degradation reaction also was determined. PNA removal efficiency in an actual sample from petrochemical industry wastewater was tested under optimal conditions. The maximum removal efficiency under the optimal conditions (pH: 7; contact time 120 min; aeration rate 10 L/min; Fe/charcoal ratio: 2/1; initial concentration of PNA: 10 mg/L) for the synthetic solution and in actual wastewater samples were 95% and 89%, respectively. In addition, the system stability was investigated in ten consecutive cycles of the electrode reuse. The removal efficiency decreased as low as 5%, which indicates the high stability of the system. The degradation process was determined to follow pseudo-first kinetics and the Langmuir-Hinshelwood model. Fe/charcoal micro-electrolysis is a relatively highly efficient system for removing PNA from wastewater and is suggested for this purpose.
Keywords: Micro-electrolysis; Fe/Charcoal; PNA; Galvanic Cells; Degradation

Aminated cassava residue-based magnetic microspheres for Pb(II) adsorption from wastewater by Xinling Xie; Jie Huang; Youquan Zhang; Zhangfa Tong; Anping Liao; Xingkui Guo; Zuzeng Qin; Zhanhu Guo (226-235).
Aminated cassava residue magnetic microspheres (ACRPM) were synthesized via an inverse emulsion method by using chemically modified cassava residue as a crude material, and acrylic acid (AA), acrylamide (AM), and methyl methacrylate (MMA) as monomers and a polyethylene glycol/methanol system (PEG/MeOH) as the porogen. Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption and vibrating sample magnetometry (VSM) were used to characterize the ACRPM. The results indicated that amino groups were grafted to the cassava residue magnetic microspheres, and the Fe3O4 nanoparticles were encapsulated in the microspheres. After porogen was added, the particle size of the ACRPM decreased from 16.5 μm to 150 nm with a pore volume of 0.05510 m3/g, and the specific surface area of the ACRPM increased from 3.02 to 12.34 m2/g. The ACRPM were superparamagnetic, and the saturation magnetization was 9.8 emu/g. The maximum adsorption capacity of Pb(II) on the ACRPM was 390 mg/g. The ACRPM exhibited a large specific surface area and provided many adsorption sites for metal ion adsorption, which favored a high adsorption capacity. Additionally, the Pb(II) adsorption process was fitted to pseudo-second-order kinetic and Langmuir isothermal adsorption models. This suggests that the Pb(II) adsorption process was dominated by a chemical reaction process and that chemisorption was the rate-controlling step during the Pb(II) removal process. In addition, the adsorbent exhibited good stability after six consecutive reuses.
Keywords: Aminated Cassava Residue; Magnetic Microspheres; Inverse Emulsion; Polyethylene Glycol/Methanol System; Pb(II); Adsorption

Facile preparation of antifouling g-C3N4/Ag3PO4 nanocomposite photocatalytic polyvinylidene fluoride membranes for effective removal of rhodamine B by Yanhua Cui; Lili Yang; Minjia Meng; Qi Zhang; Binrong Li; Yilin Wu; Yunlei Zhang; Jihui Lang; Chunxiang Li (236-247).
A simplified strategy for facilely fabricating antifouling graphite carbon nitride/silver phosphate (g-C3N4/Ag3PO4) nanocomposite photocatalytic polyvinylidene fluoride (PVDF) porous membranes was developed for effective removal of rhodamine B (RhB). g-C3N4/Ag3PO4 heterojunction was strongly fixed to the interior of the PVDF membranes via phase inversion method. The membrane structure was analyzed by Fourier transform spectrophotometer (FT-IR). The morphology of the prepared membranes was investigated using scanning electron microscopy (SEM), EDX-mapping and atomic force microscopy (AFM), respectively. All prepared nanocomposite photocatalytic PVDF membranes exhibited a typically porous structure, and g-C3N4/Ag3PO4 nanocomposites were well dispersed inside the membranes. The obtained g-C3N4/Ag3PO4 heterojunction nanoparticle decorated PVDF membrane had a lower water contact angle of 79° and higher porosity of 85% than that of other two control membranes. The nanocomposite photocatalytic PVDF porous membranes had extremely high permeation flux over 1,083 L·m-2·h-1, and could be used for the removal of RhB. The removal efficiency of g-C3N4/Ag3PO4-PVDF membranes towards RhB solution under visible light irradiation reached 97%, higher than that of the pure PVDF membranes (41%) and g-C3N4-PVDF membranes (85%). Remarkably, the flux performance and flux recovery ratio (FRR) of membranes revealed that the g-C3N4/Ag3PO4-PVDF membranes could recover high flux after fouling, which presented better fouling resistance. Furthermore, the fabricated antifouling g-C3N4/Ag3PO4 nanocomposite photocatalytic PVDF porous membranes exhibited excellent recyclability. Therefore, it is expected that g-C3N4/Ag3PO4-PVDF membranes could provide an energy-saving strategy for effective removal of organic dyes wastewater and have a great potential for practical wastewater treatment in the future.
Keywords: g-C3N4/Ag3PO4 Heterojunction; PVDF Membranes; Removal RhB; Anti-fouling Properties

Application of lab-scale sequencing batch (SBR) and sequencing batch biofilm reactors (SBBR) for treatment of dairy wastewater was investigated under organic loading of 1,130-1,560 gBOD5/m3·d. The main characteristics of the dairy wastewater were: pH=4.9, chemical oxygen demand (COD)=16,264 mg/l; biological oxygen demand (BOD5)=10,536 mg/l, PO4-P=342 mg/l; total nitrogen (TN)=224 mg/l. SBBR was filled with the Kaldnes K1 biocarrier at 30% of the volume of empty reactor. The SBR and SBBR were operated in fixed 24 h cycles, each consisting of 30 min fill up, 22 h aeration, 1.5 h settle, 30 min decant, and idle with a hydraulic retention time (HRT) of 8 days. Operational parameters such as pH, dissolved oxygen (DO), mixed liquor suspended solid (MLSS), solids retention time (SRT) and sludge volume index (SVI) were monitored during the whole cycle. The effects of these parameters on the COD, nitrogen and phosphorus removal were discussed in this paper. As a result, adding biocarrier to the reactor had a positive effect on organic with COD removal of 63.5% for SBR and 81.8% for SBBR and nutrient removal with ammonium removal of 66.0% for SBR and 85.1% for SBBR in treatment of dairy wastewater.
Keywords: COD Removal; Dairy Wastewater; Biocarrier; Nutrient Removal; SBR; SBBR

A hydrophilic-oleophobic chitosan/SiO2 composite membrane to enhance oil fouling resistance in membrane distillation by Fatemeh Ardeshiri; Ahmad Akbari; Majid Peyravi; Mohsen Jahanshahi (255-264).
To develop an inexpensive and simple technology and increase anti-oil fouling resistance for membrane distillation applications, a hydrophilic/oleophobic nanocomposite membrane was fabricated by using SiO2/Chitosan (CT) sol solution coating with different volume ratios (0.5 : 1, 1 : 1 and 2 : 1 v/v) on PVDF membrane surface. The formation of SiO2/CT layer on membrane surface was confirmed by Fourier transform infrared (FTIR) spectroscopy and energy-dispersive X-ray spectroscopy (EDX). The influence of hydrophilic nanocomposite layer on the characteristics of membranes, including in-air water contact angle, morphology, porosity, liquid entry pressure of water (LEPw) and direct contact membrane distillation (DCMD) performance, was investigated. The results show that the composite membrane (SiO2/CT (1 : 1 v/v)- PVDF membrane) by adding of 0.5 and 1 g/L gasoline concentrations not only incurred fouling but also a higher flux with respect to the neat membrane in each gasoline concentration. During 8 hours continuous desalination process of saline gasoline emulsion solution (20 gr/L NaCl solution containing 0.5 gr/L gasoline), it was found that all modified membranes had high performance stability in comparison with the neat membrane, the modified membrane showed high performance stability and flux without decreased salt rejection (99.9%). At the end, we conducted performance comparison between the prepared membranes in current work and presser based process.
Keywords: Hydrophilic-oleophobic Nanocomposite; SiO2/CT Sol Solution; Anti-oil Fouling Resistance; DCMD Performance

Development of sequential batch ozonated adsorptive membrane bioreactor to mitigate fouling with reduced energy consumption by Kavitha Nagarasampatti Palani; Darshini Saravanan; Kamalakannan Vasantha Palaniappan; Shanmuga Sundar; N. Balasubramanian (265-271).
The present study focuses on overcoming the drawback as fouling in a membrane bioreactor (MBR), which can be alleviated by integrating advanced oxidation process, adsorption, and biofilm carriers in the activated sludge process. The optimal sludge retention time, carbon and ozone dosage was 150 minutes, 15 g and 1.5 Lmin-1, respectively. The percentage removal was observed to be above 90% for chemical oxygen demand and total organic carbon whereas for total dissolved solids was only 40% under transmembrane pressure of 20 kPa. The increase in permeate flux was 30% as compared to MBR. Sequential batch membrane bioreactor (SBMBR) showed 12% reduction in energy consumption for three hour operation at the flow rate of 0.72 L/h (transmembrane pressure 20 kPa), and it was confirmed in the SEM of carbon, membrane, UV, CV and HPLC also. The energy consumption required also confirms the less internal fouling via the extended backwash of four hours.
Keywords: Sequential Batch Reactor; Biofilm Carriers; Activated Carbon; Ozonation; Permeate Flux; Activated Sludge Process

Horopito (Pseudowintera colorata) contains polygodial as an active compound that has many health beneficial properties. The potential of applying a continuous pulsed electric field (PEF) as a pretreatment step prior to solvent extraction of polygodial from Horopito leaves was studied. Horopito leaves suspended in water were subjected to PEF at electric field intensity ranging from 5 to 25 kV/cm and pulse frequencies from 200 to 800Hz. The interaction between electric field intensity and pulse frequency was found to have a significant role in extraction. Both electro-permeabilization and temperature increase from treatment caused some polygodial leaching from the leaves prior to solvent extraction. The study revealed that PEF at low electric field intensity and high frequency is the most effective way to achieve higher solvent extraction yield while minimizing the effect of leaching. The maximum improvement was obtained when PEF at 5 kV/cm and 800Hz for 348 μs were applied, giving a polygodial extraction yield of about 16.6% higher than that of non-PEF treated leaves.
Keywords: Extraction; Horopito (Pseudowintera colorata); Polygodial; Pulsed Electric Field

One-pot preparation of LiFePO4/C composites by Juan Wang; Ji-Yu Li; Zhong-Bao Shao; Hong-Tao Fan; Hong-Qiang Ru; Shu-Yan Zang (281-286).
A convenient one-pot method, called high-temperature high-energy mechanical force (HTHEMF), was successfully developed for the preparation of LiFePO4/C composites. Upon the combination of high-temperature with high-energy mechanical force, the whole synthesis process of this method is very simple and only involves two steps, the precursor preparation and the calcination step. The results of XRD, SEM, BET and electrochemical performance tests indicated that after calcination at 600 °C for 9 h, the LiFePO4/C composites have the best properties. The discharge capacity of the composites was 150.3mA h g-1 at 0.1 C. After 30 cycles test, the reversible capacity was 147 mA h g-1 and the retention ratio to the initial capacity was 97.8%. The results indicated that LiFePO4/C composites with good properties can be obtained by one-pot HTHEMF method.
Keywords: LiFePO4/C Composites; Cathode Material; High-temperature High-energy Mechanical Force; One-pot

We studied the synthesis, characterization clarification, and dye adsorption ability of chromium-based metal-organic framework (Materials Institute Lavoisier: MIL-101(Cr)). MIL-101(Cr) with 1 : 1 molar ratio of metal to ligand was ultrasound-assisted green synthesized in a DMF-free way and its adsorption capacity for pollutant remediation was studied. Several analyses were applied to clarify the characterization of materials, including TGA, SEM, XRD, FTIR, BET, and Zeta potential. Direct Red 80 (DR80) and Acid Blue 92 (AB92) were used to make model dye bearing wastewater. Response surface methodology (RSM) historical modeling was applied to the data to achieve an accurate model of the experiment. Adsorption kinetics and isotherms models were fully studied. The powerful adsorbent was the MIL- 101(Cr) with the M/L=1 : 1, which represented the high specific surface area (SSA) of 2,420 m2/g and surface charge of +27.2 mV. The maximum adsorption capacity was obtained 227 mg/g for DR80 and 185 mg/g for AB92. With an eye to the real-world application, the synthesized adsorbent well operated by removing dyes from the wastewater and high reusability after four cycles.
Keywords: Ultrasound-assisted Green Synthesis; High Specific Surface Area; MIL-101(Cr); Pollutant Remediation; RSM

This study proposes an in situ accelerated stress test of a gas diffusion layer (GDL) at a gas-solution-electrode triple phase boundary to individually examine electrochemical and mechanical GDL aging for the first time. Electrochemical GDL stability during repeated potential jumps and mechanical GDL robustness during inert gas permeation were investigated. A Pt-loaded GDL was used to mimic a GDL in contact with Pt particles at the cathode. It was also used to evaluate GDL degradation during an accelerated stress test. In this study, the GDL that experienced an electrochemical stress of potential jumps up to 1.75 V for 27.8 h exhibited 2.9-fold and 4-fold higher losses in electrochemical surface area and oxygen reduction current, respectively, than did one eroded by Ar permeation at 325 cm3 min-1 for 100 h.
Keywords: Proton Exchange Membrane Fuel Cell; Gas Diffusion Layer; In situ Accelerated Stress Test; Electrochemical and Mechanical Degradation

The effects of GaAs substrate off-orientation on GaInP/AlGaInP heterojunction solar cells were investigated. The performances of solar cells fabricated on 2° and 10° off GaAs substrates were compared. The short circuit current densities were 10.44 mA/cm2 for the 10° off sample, 7.15 mA/cm2 and 7.41 mA/cm2 for the 2° off samples, which showed 30% higher short-circuit current density for 10° off samples. Also, 30% higher external quantum efficiencies and smooth surface morphology were observed in the solar cell fabricated on the 10° off GaAs substrate. Secondary ion mass spectrometry depth profiles showed that the solar cells on 2° off substrates had a 20-times higher oxygen concentration than the solar cells on 10° off GaAs substrate in the n-GaAs/GaAs buffer layer. The 30% reduction for the solar cells on 2° substrates in short circuit current density (J sc ) was attributed to the higher oxygen concentration of the 2° off samples than the 10° off samples. I-V characteristics comparison between different front contact grid patterns was also performed for optimization of grid contacts. A 0.47 V bandgap-voltage offset, one of the device performance figures of merit to compare PV cells with different materials, was obtained.
Keywords: Heterojunction Solar Cell; Substrate Off-orientation; Impurity Incorporation; GaInP/AlGaInP

Mesoporous carbon nanofiber engineered for improved supercapacitor performance by Subrata Ghosh; Wan Dao Yong; En Mei Jin; Shyamal Rao Polaki; Sang Mun Jeong; Hangbae Jun (312-320).
Carbon nanofiber is a well-known carbon nanostructure employed in flexible supercapacitor electrode. Despite recent developments, improvement in the performance of carbon nanofiber-based electrode is still the subject of intense research. We investigated the supercapacitor performance of porosity-induced carbon nanofibers (CNFs). The fabrication process involves electrospinning, calcination, and subsequent etching. The porous CNF not only delivers a higher capacitance of 248 F/g at a current density of 1 A/g, but also exhibits a higher rate performance of 73.54%, lower charge transfer resistance and only 1.1% capacitance loss after 2000 charge-discharge cycles, compared to pristine CNF. The excellent electrochemical behavior of porous CNF is correlated with the degree of graphitization, a higher volume of mesopores, and enhanced surface area. The as-fabricated symmetric device comprising porous CNF exhibits an energy density of 9.9 Wh/kg, the power density of 0.69 kW/kg and capacitance retention of 89% after 5000 charge-discharge cycles. The introduction of porosity in CNFs is a promising strategy to achieve high-performance supercapacitor electrode.
Keywords: Supercapacitor; Porous Carbon Nanofiber; Electrospinning; Specific Capacitance; Tandem Cell