Photochemical Degradation of Aqueous Polyvinyl Alcohol in a Continuous UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> Process: Experimental and Statistical Analysis

Polyvinyl alcohol (PVA), being a dominant contributor of total organic carbon (TOC) in textile wastewater, is not easily degradable by conventional methods of wastewater treatment. This study investigates the degradation of aqueous PVA in a continuous UV/H₂O₂ photoreactor since the feeding strategy of hydrogen peroxide proves to have considerable effects on the process performance. Response surface methodology involving the Box–Behnken method is adopted for the experimental design to study the effects of operating parameters on the process performance. Experimental analysis shows that the TOC removal varies from 16.11 to 42.70 % along with a reduction of the PVA molecular weights from 56.7 to 95.3 %. The TOC removal is significantly lower than the molecular weight reduction due to the generation of the intermediate products during oxidation. Operating the UV/H₂O₂ process in a continuous mode facilitates the degradation of highly concentrated polymeric solutions using a relatively small hydrogen peroxide concentration in the feed with a small residence time ranges from 6.13 to 18.4 min.     

Photocatalytic Degradation of Poly(Vinyl Alcohol) on Pt/TiO<Subscript>2</Subscript> with Fenton Reagent

In this research Fenton reagent (Fe²⁺/H₂O₂) was investigated as oxidants to degrade poly (vinyl alcohol) (PVA). The role of nano-TiO₂ photocatalyst was discussed as an additive in Fenton reagent (Fe²⁺/H₂O₂). Pt/TiO₂ composites were also synthesized by photo-reaction to be used as additive in Fenton reagent. The rapid degradation of PVA was obtained when Pt/TiO₂ composites served as photocatalyst. The different photocatalytic efficiency of Pt/TiO₂- Fenton reagent (Fe²⁺/H₂O₂) was studied compared with TiO₂- Fenton reagent (Fe²⁺/H₂O₂) during the degradation of PVA.     

Green Synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Cellulose/Polyvinyl Alcohol Hybride Aerogel and Its Application for Dye Removal

A novel Fe₃O₄/cellulose–polyvinyl alcohol (PVA) aerogel was successfully synthesized by an eco-friendly and facile method in this work. Cellulose/PVA matrix was prepared through an environmental friendly physical cross-linking process and further in-situ decorated with Fe₃O₄. Series of Fe₃O₄ decorated aerogels were prepared and the effects of Fe₃O₄ nanoparticles (NPs) on the aerogels were systematic investigated. As-prepared aerogels exhibited desirable properties including nanostructure, relatively high porosity, improved mechanical and superparamagnetism. The TEM results showed that Fe₃O₄ NPs were integrated in the three-dimensional matrix of cellulose/PVA with a diameter of 9–12 nm. Furthermore, the mechanical strength of the aerogels was significantly enhanced after the introduction of Fe₃O₄ NPs. Meanwhile, the obtained Fe₃O₄/cellulose/PVA aerogel exhibited excellent adsorption performance toward methyl blue dye, and can be reused through fenton-like catalysts oxidative degradation of organic dye in H₂O₂ solution. Therefore, they will have a great potential application as eco-friendly and economical adsorbents.     

Reductive decomposition of waste gypsum with SiO<Subscript>2</Subscript>, Al<Subscript>2</Subscript>O<Subscript>3</Subscript>, and Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> additives

From the point of view of a sustainable and environment-friendly society based on the recycling of material resources, it is preferable to utilize waste gypsum as a substitute for lime, which is currently produced by the calcination of limestone. In the present work, the reductive decomposition of CaSO₄ was investigated under an atmosphere of CO: 2 vol%, CO₂: 30 vol%, with N₂ as a carrier gas without and with the addition of SiO₂, Al₂O₃, or Fe₂O₃. It was found that the decomposition temperature of CaSO₄ was significantly reduced from 1673 K to 1223 K when only 5 wt% Fe₂O₃ was added to CaSO₄. In the case of the addition of SiO₂ or Al₂O₃ to CaSO₄, the decomposition temperature was reduced from 1673 K to 1623 K. This was due to the formation of composite oxides (calcium ferrite, calcium silicate, or calcium aluminate) during the reaction of CaSO₄ with the additives at a lower temperature. In addition, the formation of unfavorable product CaS was inhibited in the presence of 5 wt% Fe₂O₃, and this inhibition effect further increased as the addition of Fe₂O₃ was increased. In contrast, no significant effect on the inhibition of CaS formation was observed on the addition of SiO₂ or Al₂O₃.     

Citric Acid and Vitamin C as Coupling Agents for the Surface Coating of ZrO<Subscript>2</Subscript> Nanoparticles and Their Behavior on the Optical,Mechanical, and Thermal Properties of Poly(vinyl alcohol) Nanocomposite Films

A series of bio-nanocomposites (BNC)s were fabricated through solution casting method. At first, the surfaces of ZrO₂ NPs were functionalized with citric acid and Vitamin C as green modifier agents. Then, PVA as polymer matrix was embedded with different contents (4, 8 and 12 wt%) of modified ZrO₂ (m-ZrO₂) NPs with the aim of ultrasonic irradiation process. The resulting BNCs were studied by various techniques. Thermal stability of obtained BNCs was enhanced after NPs’ addition to the PVA matrix. Optical activity of these new BNCs makes them potential candidate for UV shielding material. Lastly, the tensile strengths of the BNCs were increased in comparison to the pure PVA.     

Preparation and characterization of mesoporous γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> recovered from aluminum cans waste and its use in the dehydration of methanol to dimethyl ether

The present study includes synthesis of two γ-Al₂O₃ samples from waste aluminum cans using a simple precipitation method. Precipitation was carried out using two different precipitating agents (i.e. NaOH and NH₄OH). The two prepared alumina samples were characterized by means of X-ray diffraction (XRD) and N₂ adsorption–desorption techniques. Surface acidity of γ-Al₂O₃ samples was measured by adsorption of two different probe molecules (i.e. pyridine and dimethyl pyridine) followed by desorption measurements using thermogravimetry (TG) and differential scanning calorimetry (DSC) techniques. Catalytic activity of the two prepared alumina samples towards the dehydration of methanol (to dimethyl ether) was studied in a fixed bed reactor at 300 °C. For comparison reasons, commercial γ-Al₂O₃ sample was, also, tested for the same catalytic reaction under the same conditions. Results showed that the alumina sample prepared using NaOH as a precipitating agent exhibited a better catalytic activity and stability compared with that prepared using NH₄OH and showed a similar activity as the commercial γ-Al₂O₃ sample.     

Removal of Reactive Blue 19 dye from synthetic wastewater using UV/H2O2 and UV/Cl advanced oxidation processes

The textile and dyeing industries are among the largest water-consuming and polluting industries in the world. The most important feature of the textile dyeing industry wastewater is its color, due to the use of colored materials. Most of these dye compounds are resistant to conventional purification methods and their biodegradation is very low through secondary purification processes, resulting in incomplete removal. Therefore, selecting the optimal method to remove these color compounds is essential. In this study, we studied the removal of an organic dye contaminant (Reactive Blue dye 19 [RB19]) using advanced oxidation processes (AOPs). For this purpose, ultraviolet (UV) mercury lamps with a wavelength of 254 nm and a voltage of W16 inside a reactor were used as an energy source. The experiments were performed in a collimated beam reactor inside a dark chamber. Two oxidizers, sodium hypochlorite (NaOCl) and hydrogen peroxide (H₂O₂), were used to remove RB19 from the artificial sewage stream. Removal of RB19 with a concentration of 20 mg/L with variable pH (5, 7, and 9), oxidant concentrations (5, 10, and 20 mg/L), and time (5, 10, 15, and 30 min) were investigated during the processes of photolysis, chemical oxidation (by H₂O₂ and NaOCl), and UV/NaOCl and UV/H₂O₂ AOPs. The photolysis process did not remove the RB19. The highest removal efficiencies of RB19 by chemical oxidation processes with NaOCl and H₂O₂, UV/NaOCl, and UV/H₂O₂ at optimal conditions (pH = 5, [oxidant] = 20 mg/L, RB19 = 20 mg/L, and radiation intensity of 1005 mJ/cm²) were 64.49%, 0.88%, 99.7%, and 13.31%, respectively. These results indicate that the hydroxyl radical was produced, under optimum conditions, more in the acidic medium; thus, the RB19 removal efficiency was higher in the acidic medium. The combination of UV rays with oxidants resulted in the production of more hydroxyl radicals and increased removal efficiency.     

Preparation of MgCr<Subscript>2</Subscript>O<Subscript>4</Subscript> from waste tannery solution and effect of sulfate,chloride, and calcium on leachability of chromium

This paper presents a study regarding the preparation of MgCr₂O₄ from waste tannery solution, and chromium leaching behavior is also investigated with varying amounts of sulfate, chloride and calcium. The phase transformation, crystallinity index and crystallite diameter were characterized using XRD, FT-IR and thermal analysis. A well-crystallized MgCr₂O₄ was successfully prepared at 1400 °C. The sintering temperature had a major impact on the formation of MgCr₂O₄ compared with sintering time. The MgCr₂O₄ phase was observed initially at 400 °C and its crystallite diameter increased with increasing temperature. The concentration of total chromium leached and Cr(VI) decreased gradually with increasing temperature. The considerable amount of Cr(VI) was found in the leachate at 300–500 °C caused by Cr(VI) intermediary products. Sulfate and chlorine could impact the transformation efficiency of chromium adversely, and chlorine has a more significant effect than sulfate. The presence of calcium disturbed the formation of MgCr₂O₄ and new chromium species (CaCrO₄) appeared, which resulted in a sharp increase in the concentration of leached Cr(VI). Incorporating Cr(III) into the MgCr₂O₄ spinel for reusable products reduced its mobility significantly. This was demonstrated to be a promising strategy for the disposal of chromium containing waste resource.     

Groundwater treatment and aquatic toxicity reduction at a chemical production site

Contaminated groundwater at a chemical antioxidant and phenolic resin chemical production site was subjected to treatability studies to develop design criteria for surface water discharge. Raw groundwater required pretreatment for total suspended solids (TSS) and color removal prior to treatment by ultraviolet light/hydrogen peroxide (UV/H₂O₂). Because of high capital and operating costs for UV/H₂O₂, biological treatment was evaluated as an alternate. Respirometric analyses showed that completely mixed activated sludge could be applied as a treatment technology to the groundwater. Biotreatment resulted in an approximately 70 percent reduction in soluble chemical oxygen demand (SCOD). Residual SCOD was recalcitrant to further biodegradation. The treated effluent was tested for aquatic toxicity using fathead minnows (Pimephales promelas) and Ceriodaphnia dubia and was found to be toxic. Toxicity reduction of biotreatment effluent was evaluated in bench-scale experiments using activated carbon adsorption, filtration, and UV/H₂O₂. Subsequent toxicity testing showed that filtration alone could reduce the bioeffluent toxicity and that residual SCOD was not the primary source of toxicity.     

Fabrication of Biodegradable Superabsorbent Using RSM Design for Controlled Release of KNO<Subscript>3</Subscript>

Present study envisaged the sequential experimental design approach for the development of biodegradable Gelatin-Tapoica/polyacrylamide superabsorbent. Percentage water uptake efficacy of candidate sample was optimized using Response Surface Methodology (RSM) design under microwave irradiation. Different process variables such as potassium persulphate and ammonium persulphate (KPS:APS) ratio, pH, reaction time concentration of acrylamide and N,N-methylene-bis-acrylamide (MBA) were investigated as a function of percentage swelling using sequential experimental design. Maximum liquid efficacy of 1550% was obtained at KPS:APS?=?1.0:0.5; acrylamide?=?7.67?×?10^?1 mol L^?1; MBA?=?1.76?×?10^?2 mol L^?1; pH 10 and time?=?110 s. The 3D crosslinked network formed was characterized using Fourier Transformation Infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning Electron Microscopic (SEM) techniques and thermal stability was ensured by Thermal gravimetric Analysis/Differential Thermal Analysis/Differential Thermal Gravimetric (TGA/DTA/DTG) studies. Superabsorbent synthesized could increase the moisture content in different type of soils and was found to enhance the water-holding capability of the soil upto 60 days in clayey, 40 days in sandy and 51 days in mixture of two soils under controlled conditions. Further, candidate polymer was investigated for the in-vitro controlled release of the KNO₃ with diffusion exponent ‘n’ was found to be 0.4326 indicating Fickian type diffusion. Also, initial diffusion coefficient (D_I?=?3.49?×?10^?5 m² h^?1) was found to be greater than the lateral diffusion coefficient (D_L?=?3.76?×?10^?6 m² h^?1) indicated rapid release of KNO₃ during initial hours with slow release afterwards. The ecofriendly nature of the synthesized polymer was also tested by conducting biodegradation studies and it was found to degrade upto 94% and 88.1% within 70 days with degradation rate of 1.34 and 1.26% per day using composting method and vermicomposting method respectively. So, the synthesized candidate polymer was found to be boon for agriculture-horticulture sector with wide applicability.     

Preparation of Water-Insoluble Antibacterial Materials with Surface-Grafted Material PSt/SiO<Subscript>2</Subscript> and Their Antibacterial Activity

Styrene (St) was graft-polymerized onto the surfaces of micro-sized silica gel particles, and the surface-grafted composite particles PSt/SiO₂ were obtained. With the surface-grafted composite particles PSt/SiO₂ as a starting material, water-insoluble antibacterial materials with quaternary ‘onium’ salt-type were synthesized via two polymer reaction steps. The grafted polystyrene was first chloromethylated, resulting in grafted particles CMPS/SiO₂, and then quaterisation (QN) and quaternary phosphonium reaction (QP) were conducted with triethylamine, tri-n-butylamine and triphenyl phosphine as reagents, respectively. Two kinds of water-insoluble antibacterial materials, QN-PSt/SiO₂ and QP-PSt/SiO₂ were prepared. Their antibacterial property was mainly investigated by using Escherichia coli (E. coli) as a model bacterium and by adopting colony count method. The relationship between the chemical structure of the antibacterial group and antimicrobial activity for the water-insoluble antibacterial materials was studied in detail, and their antibacterial mechanism was investigated by TTC-dehydrogenase activity determination and extracellular DNA and RNA measurement methods. The experimental results show that QN-PSt/SiO₂ and QP-PSt/SiO₂ possess strong antibacterial activity. The main factors affecting the antibacterial ability of the water-insoluble materials are the chemical structure of the antibacterial groups, the bound density of the antibacterial groups on the surface of the water-insoluble antibacterial materials as well as the pH value of the medium. QP-PSt/SiO₂ has stronger antibacterial activity than QN-PSt/SiO₂; the QN-PSt/SiO₂ prepared with tri-n-butylamine has stronger antibacterial activity than that prepared with triethylamine; the water-insoluble material with higher bound density of the antibacterial groups has stronger antibacterial ability; as the pH value of the medium is over the isoelectric point of E. coli, the antibacterial ability is strengthened with the increase of pH value.     

Sonophotocatalytic Degradation of Chitosan in the Presence of Fe(III)/H2O2 System

The degradation of chitosan by means of ultrasound irradiation and its combination with homogeneous photocatalysis (photo-Fenton) was investigated. Emphasis was given on the effect of additive on degradation rate constants. 24 kHz of ultrasound irradiation was provided by a sonicator, while an ultraviolet source of 16 W was used for UV irradiation. To increase the efficiency of degradation process, degradation system was combined with Fe(III) (2.5 × 10⁻⁴mol/L) and H₂O₂ (0.020–0.118 mol/L) in the presence of UV irradiation and the rate of degradation process change from 1.873 × 10⁻⁹−6.083 × 10⁻⁹ mol^1.7 L s⁻¹. Photo-Fenton process led to complete chitosan degradation in 60 min with the rate increasing with increasing catalyst loading. Sonophotocatalysis in the presence of Fe(III)/H₂O₂ was always faster than the respective individual processes. A synergistic effect between ultrasound and ultraviolet irradiation in the presence of Fenton reagent was calculated. The degraded chitosans were characterized by X-ray diffraction (XRD), gel permeation chromatography (GPC) and Fourier transform infrared (FT-IR) spectroscopy and average molecular weight of ultrasonicated chitosan was determined by measurements of intrinsic viscosity of samples. The results show that the total degree of deacetylation (DD) of chitosan change, partially after degradation and the decrease of molecular weight led to transformation of crystal structure. A negative order for the dependence of the reaction rate on total molar concentration of chitosan solution within the degradation process was suggested. Results of this study indicate that the presence of catalyst in the reaction medium can be utilized to reduce molecular weight of chitosan while maintaining the power of irradiated ultrasound and degree of deacetylation.     

Synthesis,Characterization and NH<Subscript>3</Subscript>/N<Subscript>2</Subscript> Gas Permeation Study of Nanocomposite Membranes

Carbon nanotubes have exceptional mechanical properties which make them very attractive for the development of composite membranes. In this research, NH₃/N₂ gas permeation behavior of flat sheet composite membranes was examined. The cellulose acetate-multiwalled carbon nanotubes composite membranes were synthesized using solution casting method. The morphology and dispersion of carbon nanotubes were observed through SEM. However, the composite membranes were also characterized using several analytical techniques such as X-ray diffraction analysis, tensile testing analysis, and thermal gravimetric analysis. Characterization of these membranes depicted that carboxylic group functionalized MWCNTs are extremely compatible with CA. The permeation experiments were performed with NH₃ and N₂ to explore the host–guest interaction of MWCNTs with chosen gases. The permeability of NH₃ was found pronounced compared to N₂. The NH₃/N₂ selectivity up to 90 was documented.     

Influence of H<Subscript>2</Subscript> on the decomposition of halides by nonthermal plasma incorporated with in situ alkaline absorption

To control the emission of halides into the environment, an experiment on the nonthermal plasma decomposition of the halides CF₄, CHF₃, C₂HCl₃, and CHClF₂ was conducted in a wire-in-tube corona reactor. It was found that the decomposition of C₂HCl₃ and CHClF₂ was easy compared with the decomposition of CF₄ and CHF₃. With the addition of H₂ in N₂ gas, the decomposition ratio of CF₄, C₂HCl₃, and CHClF₂ increased. In contrast, the decomposition ratio of CHF₃ in a hydrogen-rich atmosphere was lower than that in an N₂ atmosphere. It was demonstrated that the yields of HF and/or HCl formed during halide decomposition clearly increased in the presence of H₂ in N₂ gas. Furthermore, in order to prevent the production of unwanted products from halide decomposition, a combination of plasma decomposition and in situ alkaline absorption was devised by coating a layer of Ca(OH)₂ onto the surface of the grounding electrode. It was demonstrated that the Ca(OH)₂ sorbent played an effective role as a scavenger, participating in halide decomposition by capturing reaction products such as HCl and HF, therefore resulting in increased halide decomposition.     

The use of waste basic oxygen furnace slag and hydrogen peroxide to degrade 4-chlorophenol

A new treatment method is developed to degrade 4-chlorophenol (4-cp) and its oxidation intermediates. The experimental results of this research demonstrate that 4-cp and its oxidation intermediates can be decomposed completely by basic oxygen furnace slag (BOF slag) with hydrogen peroxide (H₂O₂) in an acid solution. The factors that effect the treatment efficiency were studied including initial concentration of 4-cp, pH of the solution, concentration of H₂O₂ and amount of BOF slag. The BOF slags are final waste materials in the steel making process. The major components of BOF slag are CaO, SiO₂, Fe₂O₃, FeO, MgO and MnO. As the BOF slag in an acid solution, FeO and Fe₂O₃ can be dissociated to produce ferrous ion and ferric ion. Ferrous ion reacts with hydrogen peroxide to form “Fenton's reagent” which can produce hydroxyl radicals (OH^.). Hydroxyl radical possession of high oxidation ability can oxidize organic chemicals effectively. Results show that 100 mg/l of 4-cp is decomposed completely within 30 min by 438.7 g/l BOF slag with 8.2 mM hydrogen peroxide in pH=2.8±0.2 solution. The COD value of the solution is reduced from 290 to 90 mg/l. The factors studied which affect the 4-cp decomposition efficiency were the hydrogen peroxide concentration, BOF slag concentration, pH of the solution and initial concentration of 4-cp. Because large amounts of Fe₂O₃ and FeO are present in the BOF slag, the BOF slag not only has a high treatment efficiency, but also can be used repeatedly.     

High Toughness and Fast Crystallization Poly(Lactic Acid)/Polyamide 11/SiO<Subscript>2</Subscript> Composites

A poly(lactic acid) (PLA)/polyamide 11 (PA11)/SiO₂ composite was mixed from PLA, PA11, and nanosilica particles through twin-screw extrusion. The PLA/PA11/SiO₂ composite was evaluated with tensile and Izod impact tests, light transmission and haze measurement, and isothermal and nonisothermal crystallization behavior determinations. The PLA/PA11/SiO₂ (97.0/3.0) composite had approximately 10.8% less ultimate tensile strength than neat PLA, but it had greater ductility and approximately ninefold greater elongation at break. A dimple morphology was observed on the fractural surface of the PLA/PA11/SiO₂ composite, indicating that the incorporation of PA11 and nanosilica particles increased the ductility of the PLA matrix. PLA with less than 3 wt% of PA11 and 0.5 phr of nanosilica particles had an Izod impact strength of 8.72 kJ/m². PA11 and nanosilica particles effectively toughened this PLA polymer; they accelerated both isothermal and nonisothermal crystallization rates and increased the crystallinities of the resulting composites under isothermal and nonisothermal crystallization processes.     

Preparation and characterization of high surface area activated carbon from pine wood sawdust by fast activation with H<Subscript>3</Subscript>PO<Subscript>4</Subscript> in a spouted bed

Activated carbons were produced from waste pine wood sawdust using fast activation with H₃PO₄ in a spouted bed. In this study, activation temperature was set as 800 °C, and activation time ranged from 1 to 15 min. Experimental results show that sawdust impregnated with higher mass ratio of H₃PO₄ would be agglomerated in spouted bed, and difficult to fluidize. Therefore, an amount of quartz sand was added to assist for good fluidization. Fluidization of particle can improve the BET surface area or micropore volume of activated carbons. High BET surface area activated carbons can be obtained with activation time of only 1–5 min by combining the fluidization and H₃PO₄ fast activation. The obtained activated carbons contained developed pore structure and abundant surface functional groups (carboxyl, carbonyl and P-containing groups) by SEM–EDS, FTIR and XPS techniques. The particles of impregnation ratio of 1:1 can achieve fluidization without adding the quartz sand, which was convenient for experimental operation and even industrial production, and the BET surface area can reach more than 1000 m²/g in activation time of only 5 min.     

Influences of Magnesium <Emphasis Type="Italic">tri-</Emphasis>Silicate on the Physical,Mechanical, and Degradable Properties of Ultraviolet (UV) Radiation Cured Plain Board Surface

A series of formulations were prepared with different percentages of oligomer, epoxy diacrylate (EA-1020 ), monomer, 1,6 Hexane diol diacrylate,(HDDA) and different percentages of filler (Magnesium tri-silicate, Mg₂Si₃O₈). Irgacure 369 [2-Benzyl-2-dimethyl-amine-1 (4-morpholinophenyl) butanone-1] was used in the formulations as photoinitiator. Ultraviolet (UV) cured thin polymer films were prepared from these formulating solutions on clean glass plates. Pendulum hardness (PH), gel content and macro scratch hardness (MSH) of the UV cured films were studied. One percent Mg₂Si₃O₈ containing formulation showed the premium properties. The substrates (plain board) were coated by these formulating solutions and cured under the same UV lamp at different intensities of radiation. Various properties of the coated surface such as PH, gloss, adhesion, abrasion and MSH were investigated. The base coat containing 1% Mg₂Si₃O₈ and top coat containing 48% HDDA produced the best performance among all the formulations inspected. The degradable properties in different weathering conditions on PH, gloss, adhesion, abrasion and MSH were measured. The surface cured with the optimized formulation (E) again yielded the minimum loss of the properties.     

H2O2/VisUV photo-oxidation process for treatment of waterborne hazardous substances—Reaction mechanism, rate model, and data for tubular flow and flow stirred tank reactors

This paper presents the chemical reaction engineering development of the H₂O₂/VisUV photo-oxidation process for treatment of hazardous waterborne substances, that occur in groundwater, leachates, and industrial wastewater. Reaction results, on benzene (BNZ), dichlorobenzene (DCB), trichloroethene (TCE), trichloroethane (TCA), and carbon tetrachloride (CTC), have been obtained, providing engineering data and models that can be used to size full-scale equipment. A photochemical flow stirred tank reactor (pcfSTR) and a photo-chemical tubular flow reactor (pcTFR) were used in the experimental work. Two experimental discoveries were made in the course of the work: (1) conventional thermal kinetics do not apply, the rate controlling variable is the photon flux, and (2) for the photo-chemical reactors used, the pcfSTR was more effective than the pcTFR. The following sub-topics are discussed: reaction mechanism, reactor hydrodynamics, photon flux effects, typical reaction data (on benzene and trichloroethane), and rate constants.     

Study on desulfurization performance of MnO<Subscript>2</Subscript>-based activated carbon from waste coconut shell for diesel emissions control

Increasing concern about the air pollution caused by sulfur dioxide (SO₂) from diesel exhaust has resulted in the improvement of low-temperature desulfurization materials for the combined SO₂ trap. In this study, coconut shell activated carbon (AC) is pretreated by nitric acid to prepare MnO₂-based activated carbon materials for SO₂ removal. The prepared materials are characterized intensively by SEM, TEM, BET, XRD, FTIR, and XPS. The SO₂ capture capacity of these materials are measured at low temperature by thermogravimetry, and the SO₂ equilibrium adsorption characteristic is also investigated. The results show that the concentrations of nitric acid do not significantly change the textural properties of MnO₂-based AC materials. The content of surface-oxygenated groups (carbonyl carbon and transition) initially increases with the HNO₃ concentration rising and reaches the maximum value when the HNO₃ concentration is 10 mol/L, resulting in the enhancement of the SO₂ capture capacity. SO₂ capture capacity of MnO₂-based activated carbon decreases after regeneration and keeps stable after several cycles of thermal regeneration. The experimental data for SO₂ adsorption on MnO₂-based AC composite can fit the Freundlich model well in comparison with Langmuir model.