Regeneration Performance Research Articles

Electrospinning prepared nickel-based carbon fibers with enhanced adsorption capacity for adsorption desulfurization of fuels

Enhanced adsorption capacity of adsorbents with excellent regeneration properties always remained the focus of researchers in the adsorptive desulfurization (ADS) technology. In this paper, we report an electrospinning method to prepare nickel-based carbon fibers (NCF), and their adsorption desulfurization performance was compared with those of nickel-based carbon particles (NCP) obtained via traditional solid-state grinding method. The results demonstrated that compared with NCP, NCF contained more abundant mesoporous specific surface area and mesopore volume, well-distributed active metal sites, which would be beneficial to their enhanced adsorption desulfurization performance. As a result, the adsorption capacity of NCF was as high as 13.13 mg S/g in the ADS of thiophene, and its regeneration performance was also far better than that of NCP. In addition, the adsorption process of thiophene was briefly analyzed from the perspective of kinetics, which demonstrated that the adsorption of thiophene in NCF and NCP were both in accordance with the pseudo-second-order kinetic model.

Solvent-Free Synthesis of Covalent Organic Framework/Graphene Nanohybrids: High-Performance Faradaic Cathodes for Supercapacitors and Hybrid Capacitive Deionization.

Covalent organic frameworks (COFs) with flexible periodic skeletons and ordered nanoporous structures have attracted much attention as potential candidate electrode materials for green energy storage and efficient seawater desalination. Further improving the intrinsic electronic conductivity and releasing porosity of COF-based materials is a necessary strategy to improve their electrochemical performance. Herein, the employed graphene as the conductive substrate to in situ grow 2D redox-active COF (TFPDQ-COF) with redox activity under solvent-free conditions to prepare TFPDQ-COF/graphene (TFPDQGO) nanohybrids and explores their application in both supercapacitor and hybrid capacitive deionization (HCDI). By optimizing the hybridization ratio, TFPDQGO exhibits a large specific capacitance of 429.0Fg-1 due to the synergistic effect of the charge transport highway provided by the graphene layers and the abundant redox-active centers contained in the COF skeleton, and the assembled TFPDQGO//activated carbon (AC) asymmetric supercapacitor possesses a high energy output of 59.4Whkg-1 at a power density of 950Wkg-1 and good cycling life. Furthermore, the maximum salt adsorption capacity (SAC) of 58.4mgg-1 and stable regeneration performance is attained for TFPDQGO-based HCDI. This study highlights the new opportunities of COF-based hybrid materials acting as high-performance supercapacitor and HCDI electrode materials.

A novel polymer coated magnetic activated biochar-zeolite composite for adsorption of polystyrene microplastics: Synthesis, characterization, adsorption and regeneration performance

A magnetic activated biochar-zeolite composite (MACZ) was produced and coated with polyethyleneglycol (PEG) and polyethylenimine (PEI) to produce (PMACZ) and enhance its electrostatic properties for the adsorption of 2 µm and 15 µm microplastics. Produced adsorbents were characterized with scanning electron microscopy and energy dispersive spectroscopy (SEM/EDS), Brunauer-Emmett-Teller (BET), zeta sizer, vibrating sample magnetometer (VSM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). Equilibrium and kinetic laboratory tests were conducted to evaluate the adsorption behaviour. A response surface analysis (RSM) was conducted on a central composite design to evaluate the effects of pH and temperature on adsorption. Zeta potential results showed PEG/PEI can induce positive charges on adsorbents. Adsorption kinetic followed a pseudo-second-order model with R2 of 99 %. The results of isotherm studies indicated a correlation with the Temkin model with a maximum R2 of 98 %. The results showed a maximum adsorption capacity of 736 mg/g and 769 mg/g for PMACZ on 2 µm and 15 µm microplastic, respectively. Optimization results indicated a pH of 4 and a temperature of 28 and 24 for maximum adsorption of 2 µm and 15 µm microplastics. ANOVA analysis showed pH has a higher impact on adsorption. The produced material can be regenerated for a minimum of 4 cycles. Also the effect of ion matrixes, sea salt, tap water and waste water effluent on adsorption of MACZ and PMACZ has been investigated.

Efficient removal of copper ions, zinc ions, and tetracycline in water by functionalized Canadian horseweed hydrothermal carbon: The combination of experiment and DFT calculation

A silicate-hydrothermal carbon composite material (GHC) was prepared by a one-step hydrothermal method using Canadian horseweed as raw material and cheap sodium silicate and magnesium sulfate as modification reagents for the adsorption of copper (Cu2+), zinc (Zn2+), and tetracycline (TC) in water. The results showed that maximum capacities of the adsorption of Cu2+, Zn2+, and TC by GHC are 211.92 mg·g−1, 224.96 mg·g−1, and 358.58 mg·g−1. TC can provide certain active sites for GHC to adsorb Cu2+ or Zn2+ in a binary system. When the concentration of Cu2+ or Zn2+ is low, i.e., <30 mg·L−1, it will promote GHC’s ability to adsorb TC. When the concentration of Cu2+ or Zn2+ is greater than 30 mg·L−1, the adsorption capacity of GHC to TC began to decrease. This may be related to the presence of too many complexes on the surface of GHC. Too many complexes will block the pores on the surface of GHC and reduce the effective adsorption sites of GHC. The different mechanisms for the adsorption of Cu2+ and Zn2+ are different from the adsorption of TC. In this study, 2D-COS and DFT calculations are used to explore these mechanisms. The results show that CO, CO, and CC are involved in the adsorption of Cu2+, Zn2+, and TC, and CO and CO have stronger capacities than CC for Cu2+, Zn2+, and TC. GHC has stable adsorption properties for Cu2+, Zn2+, and TC in different water samples, and has good regeneration performance. Thus, GHC is an economical and efficient adsorbent with good application potential.

Chitosan-based molecularly imprinted sponge for selective recognition and recycling of dibenzothiophene from diesel

Recycling of high value-added dibenzothiophene (DBT) from diesel using adsorption technology is a convenient and economical strategy to realize “Resources Reuse”, but the conventional adsorbents have the disadvantages of low adsorption selectivity and difficult retrieval. Herein, in this study, we elaborately designed and constructed a chitosan-based molecularly imprinted sponge (CS-MIS) with three-dimensional network structure via a bulk polymerization-lyophilization protocol. Batch adsorption experiments were conducted three replications to appraise the potential of CS-MIS for DBT adsorption. The influence of adsorbent dosage, initial DBT concentration, adsorption time and temperature on the adsorption performance were systematically investigated. The adsorption experimental results showed that CS-MIS exhibited a superior maximum adsorption equilibrium capacity of 15.17 mg/g for DBT compared to the chitosan-based non-imprinted sponge (CS-NIS; 6.34 mg/g). The DBT adsorption on CS-MIS coincided well with the pseudo-second-order kinetic and Langmuir isotherm models. The selective tests in the presence of multiple interfering molecules indicated the remarkable selective recognition of CS-MIS toward DBT with the relative selectivity coefficients for benzothiophene, indole, and fluorene of 1.99, 2.28, and 1.41, respectively. The notable selectivity of CS-MIS for DBT adsorption were mainly attributed to the imprinted sites matched well with DBT geometry on the surface of CS-MIS. Additionally, CS-MIS exhibited the excellent regeneration performance.

Three-Dimensional Porous PVDF Foam Imprinted Membranes with High Flux and Selectivity toward Artemisinin/Artemether.

In this study, a new 3D porous PVDF-foam-imprinted membrane (PPIM) for the selective separation of artemisinin (ART) was first prepared via the dopamine adhesion of pre-synthesized MIPs into the interior of the PPIM. In the PPIM, the pre-synthesized molecularly imprinted polymers (MIPs) with artesunate (ARU) as a dummy template were uniformly loaded on the interior of the membrane, avoiding the defects of recognition site encapsulation found in the conventional membrane. This membrane also exhibited excellent flux, which is beneficial in practical separation applications. The PPIM was systematically characterized via FT-IR, SEM, pore-size distribution analysis, water contact angle test, membrane flux, and mechanical performance analysis, respectively. In the static adsorption experiment, the pseudo-second-order kinetic model better fitted the rebinding data of ART. Under dynamic conditions, the ART adsorption capacity of the PPIM could be further remarkably improved by tailoring the flow rate to 3 mL min-1. In the selective separation experiment, with artemether (ARE) as the competition substrate, the selective separation ability (α) of the PPIM towards ART/artemether (ARE) reached its peak value (3.16) within only 10 min at this flow rate, which is higher than that of porous PVDF foam non-imprinted membranes (PPNM) (ca. 1.5), showing great separation efficiency in a short time. Moreover, the PPIM can be reused five times without a significant decrease in its adsorption capacities, showing good regeneration performance. This work highlights a simple strategy for constructing new MIMs with high flux and great mechanical strength to achieve the efficient selective separation of ART and ARE in practical applications.

DEVELOPING SUSTAINABLE URBAN REGENERATION (SUR) EVALUATION METHOD FOR THE MALAYSIAN CONTEXT

Sustainable urban regeneration (SUR) represents an advanced and comprehensive approach to urban regeneration, aiming to integrate the three key pillars of sustainable development. While various global framework exist for measuring sustainable urban regeneration performance, a dedicated method tailored to the specificities of the Malaysian context remains absent. This study addresses this gap by developing SUR evaluation method for Malaysia, utilising indicators as a means to gauge sustainability performance. A self-administered questionnaire was employed to solicit assessments from key experts regarding potential SUR criteria and indicators. The resulting data were analysed using the Analytic Hierarchy Process (AHP) to establish weightage based on priority scales. Results from the study identified ten (10) fundamental criteria and thirty-three (33) indicators, each assigned respective weightage, pivotal in achieving sustainable urban regeneration. This study contributes to the improvement of sustainability performance of urban regeneration initiatives in Malaysia by introducing a novel evaluation method. As a way forward, it is recommended that the practicality and capability of the proposed evaluation method be assessed through real-life case study in Malaysia.

Defective UiO-66 metal–organic gels for optimizing gaseous toluene capture

Developing high-performance sorbents for volatile organic compounds (VOCs) is urgently required for environmental cleaning and personnel protection. Zirconium-based metal–organic frameworks (Zr-MOFs) have been deemed attractive candidates for gaseous toluene capture due to their superior stability and high adsorption capacity. However, the practical application of powdered Zr-MOFs is hindered by inherent limitations. Here, we report a series of defective UiO-66 metal–organic gels (G66-X) with variable missing linker deficiency by altering the modulator concentration. The defect concentration of the adsorbents has a significant impact on the porosity and gaseous toluene adsorption capacity. Dynamic breakthrough results reveal that G66-9 demonstrates optimal breakthrough time of 336 min/g and uptake amount of 334 mg/g, outperforming those of many other typical toluene adsorbents. The breakthrough times and the uptake capacities dramatically decrease with the increase of adsorption temperature. An outstanding regeneration performance of adsorbents can almost maintain even after five adsorption–desorption cycles.

Polyester conversion by homogeneous catalysis for separating and recycling ammonia from biogas

Biogas is being promoted as a renewable and clean energy source. However, NH3 is a precursor of NOx and PM2.5 within the biogas, threatening ecological and human health. Therein, recycling waste NH3 from the biogas as a raw material of nitrogen fertilizer was tested by optimizing polyester as a sorbent material. After homogeneous catalysis, the converted polyester significantly increased the NH3 adsorption sites within polyester nanopores; correspondingly, the NH3 adsorption capacity increased from 0.56 mg·g−1 to 84.07 mg·g−1. Based on the structural characterization of polyesters, functional groups analysis before and after adsorption, and kinetic analysis during adsorption, chemical adsorption was identified as the dominant mechanism for NH3 adsorption. Moreover, selective adsorption and the regeneration experiments to optimize polyester indicated that NH3 could be efficiently separated from biogas with good regeneration performance. The results demonstrate the efficacy of recycling waste polyester and NH3 from the biogas.

Uranium recovery from weakly acidic wastewater using recyclable γ-Fe2O3@meso-SiO2

U(VI)-containing acidic wastewater produced from uranium mining sites is an environmental hazard. Highly efficient capture of U(VI) from such wastewater is of great significance. In this study, a mesoporous core–shell material (i.e. γ-Fe2O3@meso-SiO2) with magnetically and vertically oriented channels was rationally designed through a surfactant-templating method. Batch experiment results showed that the material had an efficiency level of >99.7% in removing U(VI) and a saturated adsorption capacity of approximately 41.40 mg/g, with its adsorption reaching equilibrium in 15 min. The U(VI) adsorption efficiency of the material remained above 90% in a solution with competing ions and in acidic radioactive wastewater, indicating its ability to selectively adsorb U(VI). The material exhibited high adsorption efficiency and desorption efficiency in five cycles of desorption and regeneration experiments. According to the results, the mechanism through which γ-Fe2O3@meso-SiO2 adsorbs U(VI) was dominated by chemical complexation and electrostatic attraction between these two substances. Therefore, γ-Fe2O3@meso-SiO2 is not only beneficial to control the environmental migration of uranium, but also has good selective adsorption and repeated regeneration performance when used to recover U(VI) from weakly acidic wastewater in uranium mining.

Selective removal of heavy metals from wastewater using polyphenol nano-microspheres: Enhancing sequestration and regeneration performance through pH-responsive coordinated structural changes

The proficient advancement of nanoscale adsorbents assumes a pivotal role in the enhanced elimination of heavy metals to trace concentrations. Nevertheless, within the realm of engineering, the attainment of elevated selectivity and effective regeneration remains an arduous endeavor. In this context, we propose a novel structure-tunable sorption/regeneration mechanism by designing TA cross-linked polyphenolic nano-microspheres (PTA). These PTAs exhibit tunable pH-responsive metal coordination structures, enabling high sequestration and purification in removing heavy metals, and facilitating efficient regeneration. Taking Pb(II) as an example, under neutral conditions, the PTAs form a six-coordination configuration with Pb(II) ions, resulting in larger selectivity of Kd: 84400 mL/g with a 99 % removal efficiency even in the presence of various cations, anions, and organic acids. This performance far surpasses that of the commercial ion exchanger D001, exhibiting an enhancement factor of nearly 250 times, rendering it amenable for deployment in a wide array of contaminated water sources, encompassing lake water and industrial wastewater. Notably, the PTA also demonstrates exceptional practical utility, affording a voluminous treatment capacity of 5250 L per kilogram of adsorbent in wastewater scenarios. Furthermore, under acidic conditions, the transformation of PTA's metal coordination into a weaker two-coordination facilitates the efficient desorption of Pb(II) with an impressive efficiency of up to 99.0 % across multiple cycles. In contrast, commercial cheated resins D401 and D418 experience a significant 70 % decrease in reuse performances after the first cycle. This study provides a new perspective and platform for efficient adsorbent development through coordinated structural changes, it holds the potential to alleviate the challenges associated with deep restoration of heavy metal-contaminated wastewater.

Dual surfactants-assisted adsorption of lithium ions in liquid lithium resources on a superhydrophilic spinel-type H4Ti5O12 ion sieve

The industrial application scope of spinel-type titanium oxide ion sieves is limited by its low adsorption efficiency and regeneration performance. In this study, H4Ti5O12 (HTO-IV), a superhydrophilic spinel-type lithium ion sieve, was synthesized for the first time with the dual surfactants of CTAB and F127 to modulate the surface morphology and surface wettability of the raw material. The prepared HTO-IV lithium ion sieve was composed of ultrathin nanosheets assembled into microspheres and showed excellent surface hydrophilicity and an open hierarchical mesoporous structure, which allowed rapid ion exchange between Li+ and H+. Li+ adsorption rate exceeded 85 % within 30 min and its maximum theoretical adsorption capacity was 57.90 mg/g. The adsorption process of Li+ on HTO-IV followed a pseudo-second-order kinetic model and Langmuir adsorption isotherm model. HTO-IV also exhibited good adsorption selectivity towards Li+ in the presence of coexisting ions. Furthermore, the lithium adsorption ratio of the HTO-IV ion sieve remained at around 97 % even after five adsorption–desorption cycles, demonstrating excellent adsorption capacity and cycling stability. The study highlights the relationship between surface hydrophilicity and adsorption performance of the adsorbent.

Iron-containing biochar derived from dyeing sludge for high-performance capacitive deionization

The design and synthesis of high-performance, environmentally friendly, and economical electrode materials are essential for the development of energy-efficient capacitive deionization (CDI) technologies. As a strategy to turn waste into resource, abundant and low-cost sludge biomass materials are promising candidates for the preparation of CDI electrodes. In this work, a series of iron-containing dyeing sludge-derived biochar with different iron compounds were successfully prepared by direct pyrolysis followed by chemical modification treatment, and applied them as hybrid capacitive deionization (HCDI) cathodes for the first time. The ion adsorption capacity of HCDI electrode is up to 78.76 mg g−1 in 500 mg L−1 NaCl solution at 1.2 V and stable regeneration performance over 50 cycles. XPS measurements reveal that the storage mechanism of ions is a pseudocapacitance effect induced by the Fe2+/Fe3+ redox couple, enabling reversible and fast ion storage. The enhanced HCDI performance is ascribed to the well dispersed iron compounds active sites, rich pore structure and superior hydrophilicity. This work offers a promising strategy for the synthesis of high-performance HCDI electrode materials from sludge biomass, and demonstrates the superior pseudocapacitive performance of Fe2+/Fe3+ redox couple.

Coke filled bed electrode coupled with vibration regeneration for efficient electrochemical water softening

The industrial application of electrochemical water softening technology is constrained by cathode surface area and regeneration issues. In this work, a three-dimensional filled-bed electrode is built by coupling stainless steel mesh with coke. The electrochemical water softening and regeneration performances are extensively investigated. The results demonstrate that coke disperses the electrode potential, enabling more rapid precipitation of calcium carbonate in circulating water where calcium and magnesium ions are present in common. The energy consumption is 8.66 KWh/KgCaCO3 and the precipitation rate is 32.74 g/m2·h at 36 A/m2. Additionally, because the coke surface is not easy to deposit scale layer, it can maintain activity when the outer stainless steel mesh is covered with scale layer. Even if the electrode is deactivated, vibration can swiftly restore it, allowing it to keep up effective water softening performance. After several regenerations, the precipitation rate is still above 30 g/m2·h.

Development of supervised machine learning model for prediction of TEG regeneration performance in natural gas dehydration

Development of supervised machine learning model for prediction of TEG regeneration performance in natural gas dehydration

Mechanism of Pd(II) adsorption by nanoscale titanium dioxide loaded bamboo shoot shell biomass.

Palladium (Pd) is widely used in catalyst, aerospace, and medical applications, but only 1% of its reserves are found in nature. So, the recovery of Pd(II) is very important. Natural fibers are a good adsorption material, and the abundant functional groups in bamboo shoot shell (BSS) fibers can form interactions with metal particles. However, few studies on Pd(II) adsorption using BSS fibers exist. In the present work, waste bamboo shoot shells were doped with titanium dioxide (TiO2) particles, and the surface activation of BSS-TiO2@CA by citric acid (CA) was carried out to prepare an efficient and recyclable adsorbent BSS-TiO2@CA for the adsorption of Pd(II). The adsorption performance, adsorption mechanism, and regeneration performance of BSS-TiO2@CA on Pd(II) were systematically analyzed by continuous adsorption experiments, characterization, and response surface method. It was found that the surface-activated waste bamboo shoot shells had an outstanding adsorption capacity of Pd(II), and the maximum adsorption rate of BSS-TiO2@CA reached 85% with a maximum adsorption capacity (Qm) of 175.74 mg/g. The functionalized use of waste bamboo shoot shells provides a new idea for the development of sustainable, cost-effective, and environmentally friendly adsorbents.

Removal of hydrocarbon pollutants from aqueous media using hydrophobic cellulose-based adsorbents

The current work was carried out to eliminate hydrocarbon contaminants from oily wastewater. The alpha-cellulose-based aerogels were synthesized by sol-gel method and hydrophobic modification was applied with methyltrimethoxysilane (MTMS) through chemical vapor deposition (CVD). The FT-IR, SEM, and BET analyses were used to characterize the adsorbents. The effects of several factors such as hydrophobic modification, alpha-cellulose weight percentage, contact time, temperature, and pollutant type on adsorption were studied. The results revealed that the maximum adsorption capacities for engine oil, crude oil, and kerosene oil and mixture (with same proportions) were 28.4, 25.2, 22.8, and 25.7 (g/g), respectively. The difference in density and viscosity are the main reasons for different adsorption capacities. The adsorption capacity increased with increasing density, as well as in higher temperatures. Lower viscosity causes easier penetration, which is eventuated in increasing the adsorption capacity. However, after 40 °C with more viscosity decrease, the release rate increased and the adsorption capacity decreased. The adsorption equilibrium time for the three oil compounds is approximately 8 min. The adsorption kinetics follows the pseudo-second-order model, showing that chemisorption dominates. Also, the thermodynamic studies showed that the adsorption was endothermic and non-spontaneous. In addition, the synthesized adsorbent showed acceptable regeneration performance up to 5 cycles.

Preparation of an Activated Carbon Composite with High Thermal Conductivity Based on Emulsified Asphalt and Carbon Nanotubes and its Adsorption Performance for n‐Hexane

AbstractActivated carbon, as the main adsorption material for treating VOCs, has been widely used. To solve the problem of safety hazards in activated carbon adsorption process due to the large amount of heat released, highly thermally conductive composite activated carbon (A‐AC/CNTs) was prepared using asphalt and highly thermally conductive carbon nanotubes (CNTs) for thermal conductivity improvement. Uniform dispersion and firm loading of CNTs in the carbon production material were achieved by dispersing carbon nanotubes (CNTs) in the asphalt‐in‐water emulsion. Experimental results showed that the specific surface area of A‐AC/CNTs reached a maximum when the loading of CNTs was 0.5 wt %. Meanwhile, the thermal conductivity increased by 1.5 times compared with the original activated carbon. The adsorption capacity of n‐hexane reached the maximum of 2868 mmol ⋅ g−1, and the adsorption capacity increased by 21.41 %. It also maintained good regeneration performance after dynamic adsorption experiments.

Combined experimental and theoretical studies on iodine capture of Zr-based metal-organic frameworks: Effect of N-functionalization and adsorption mechanism

The potential leakage of nuclear waste, especially radioiodine, is a major safety concerning issue around the world. To remove radioiodine from nuclear waste efficiently, there is an urgent demand for adsorbents that possess both high stability and strong adsorption affinity for environmental remediation. Herein, two Zr-based metal-organic frameworks (Zr-MOFs) and their N-functionalized analogs have been synthesized and researched for iodine adsorption in both vapors and solutions. It was found that Zr-MOFs with N-enriched ligands (e.g., pyridine and amino) exhibited the faster iodine adsorption rate and the higher iodine uptake amount (e.g., reaching adsorption equilibrium within 4 h with the removal rate of above 85 % for iodine solution adsorption) than their unfunctionalized counterparts (UiO-66 and UiO-67). The critical role played by N-enriched groups in enhancing iodine adsorption has been revealed through versatile model fittings, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy characterizations, as well as density functional theory (DFT) calculations. Compared to those in amino group, the N-atoms in pyridine groups showed a deeper affinity toward iodine molecules. Remarkably, the N-enriched UiOs adsorbents also exhibited good recyclability, especially UiO-66-PYDC and UiO-67-NH2, which could maintain the removal efficiency of 89.05 % and 85.49 % after four adsorption-desorption recycling tests. With the strong iodine uptake affinity and outstanding regeneration performance, this work has systematically investigated the impact of N-functionalization on the enhanced performance for iodine capture by using the N-enriched UiO MOFs as promising adsorbents, providing an insightful guideline into the physical chemistry of adsorption mechanism behind the radioiodine capture.

Synthesis of Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;/UiO-66-NO&lt;sub&gt;2&lt;/sub&gt;/TFC-PA catalytic film for removal of organic pollutants from aqueous solutions

A novel catalytic film of Fe2O3/UiO-66-NO2/TFC-PA was successfully synthesized via the conventional polymerization technique. The as-fabricated sample was characterized by XRD, FT-IR, UV-Vis DRS, and N2 adsorption-desorption isotherm. The catalytic activity of the film was examined by degradation of Methylene blue (MB) under irradiation of visible light. The synthesis conditions of the film were studied as well. The results illustrated that under optimal synthesis conditions as the Fe2O3/UiO-66-NO2 amount of 0.01 g, the polymerization time of 30 s, the catalytic particles were dispersed in the TMC solution and the TMC concentration was 0.1%, the film exhibited a MB removal percentage of 95 %. The material also showed an outstanding regenerative performance with the treatment efficiency reaching 92.8% after four regenerations. The kinetic results showed that the photocatalytic degradation of MB over the film followed the first-order kinetic model.