Zinc Oxide-Catalysed Photo-Oxidative Degradation of Chlorophenols

Chlorophenols are priority pollutants that must be eradicated from the environment owing to the severity of their toxicity and resistance to traditional treatment. Photocatalytic oxidation is an advanced oxidation method which has proven reliability to eliminate persistent pollutants from air and water. The activity of zinc oxide for pollutant removal by photocatalytic oxidation has been well established. In this work the photocatalytic transformation of 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol in irradiated ZnO suspensions at 299 K was studied. The effect of operating parameters such as catalyst and concentration doses on the decomposition rate of these para-chlorinated compounds has been investigated and optimised. It was discovered that the optimum feed concentration for the phenolic compounds is 50 mg L-1. The optimum amount of ZnO was determined for the degradation of 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol which decreased as with increasing of chlorine substituent. For 4-chlorophenol degradation the first clearer description of the effect of doses using response surface was reported. Kinetic profiles on the decomposition of chlorophenols over ZnO were consistent with pseudo-zeroeth order rate scheme. For 2,4-dichlorophenol and 2,4,6- trichlorophenol the decomposition was slow at the short irradiation time. It was found that the degradability of chlorophenols increased as the number of ringchlorine increased. The effect of pH on the destruction rate was found to be influenced by chlorophenol adsorption and dissociation equilibrium. The effect of different anions on the rate of chlorophenol degradation was evaluated by utilising sodium salts as additives. Except for 4-chlorophenol it was found that, inorganic anion additives such as SO4 2-, S2O8 2- and Cl- demonstrated inhibition to the decomposition rate of chlorophenol. HPO4 2- was found to show strongest inhibition and could even hamper the degradation of 4-chlorophenol. The progression of intermediates during the mineralisation of chlorophenols was chromatographed on high performance liquid chromatograph (HPLC). The structure elucidation of pathway products en route to mineralisation of chlorophenols was performed by the combined gas chromatography-mass spectrometry (GC-MS) and HPLC methods. The study disclosed some hitherto unreported intermediates of photocatalytic decomposition of 4-chlorophenol and 2,4-dichlorophenol. Catechol was detected as new intermediate of 4-chlorophenol degradation. Similarly, 4- hydroxybenzaldehyde, benzoquinone and 4-chlorophenol are for the first time reported for 2,4-dichlorophenol degradation. The work also revealed the intermediates of 2,4,6-trichlorophenol which have not been in literature. It is highlighted herein the mechanism of formation of all pathway intermediates

Heterogeneous photocatalytic degradation of organic contaminants over titanium dioxide: A review of fundamentals, progress and problems

Even though heterogeneous photocatalysis appeared in many forms, photodegradation of organic pollutants has recently been the most widely investigated. By far, titania has played a much larger role in this scenario compared to other semiconductor photocatalysts due to its cost effectiveness, inert nature and photostability. Extensive literature analysis has shown many possibilities of improving the efficiency of photodecomposition over titania by combining the photoprocess with either physical or chemical operations. The resulting combined processes revealed a flexible line of action for wastewater treatment technologies. The choice of treatment method usually depends upon the composition of the wastewater. However, a lot more is needed from engineering design and modelling for successful application of the laboratory scale techniques to large-scale operation. The present review paper seeks to offer an overview of the dramatic trend in the use of the TiO2 photocatalyst for remediation and decontamination of wastewater, report the recent work done, important achievements and problems

Adsorption of Aqueous Using Granular Adsorbents from Accanthospermum hispendum DC

Granular activated carbons have been important adsorbents for the decontamination of aqueous environmental contaminants. Acanthospermum hispidum weed represents a ready available source of low-cost adsorbents in sub-Saharan Africa that has barely been paid attention. The effects of pH, contact time, concentration, adsorbent dosage, particle size and temperature on the adsorptive removal of Pb (II) from aqueous solutions over activated carbon granules from the thorns of Accanthospermum hispindum (AC-T) were for the first time investigated and compared with those of the leaves (L), the sodium hydroxide modified thorns (NaOH-T) and regular thorns (T) of this plant. These adsorbents were characterised by the surface charge analysis, scanning electron microscopy (SEM) and the Attenuated Total Reflectance Fourier Transform infrared (ATR FTIR) spectroscopy. The SEM revealed a wafer-like appearance for the AC-T with a large distribution of open pores. The adsorption data of lead uptake onto the adsorbents were examined using two pseudo-order kinetic schemes and three isotherm models. To fully understand the adsorption capacities of the adsorbents, batch desorption recoveries were studied. The FTIR depicted the various functionalities responsible for the adsorption. Adsorption over AC-T was found to agree with pseudo second-order kinetic scheme, the Langmuir and Freundlich isotherm. This material exhibited the highest adsorption capacity. The order of reusability of the adsorbents is T < AC-T < NaOH-T

Photocatalytic removal of 2,4,6-trichlorophenol from water exploiting commercial ZnO powder.

2,4,6-trichlorophenol is an important water pollutant owing to the severity of its toxicity. The aqueous phase photocatalytic oxidation of 2,4,6-trichlorophenol over ZnO was investigated as a potential method for the abatement of this pollutant. The effects of operating parameters such as initial ZnO doses and substrate concentration on the removal of 2,4,6-trichlorophenol were studied and optimised at 0.75 g L− 1 and 50 mg L− 1, respectively. The photocatalytic system afforded the highest degradation efficiency at neutral pH. The decomposition of 2,4,6-trichlorophenol by the photoprocess agreed satisfactorily with pseudo zero-order kinetic model. The effect of the presence of SO42−, S2O82−, HPO42− and Cl− on the 2,4,6-trichlorophenol removal rate was for the first time revealed. Some hitherto unreported pathway intermediates of ZnO-assisted 2,4,6-trichlorophenol degradation were recorded using gas chromatography–mass spectrometry (GC–MS) and high performance liquid chromatography (HPLC). A tentative reaction mechanism for the formation of these intermediates was proposed

Sol-gel synthesis of Fe₂O₃-doped TiO₂ for optimized photocatalytic degradation of 2,4- dichlorophenoxyacetic acid

Fe₂O₃-doped and undoped TiO₂ catalysts were synthesized by sol-gel method and used to optimize the photocatalytic degradation of 2,4-Dichlorophenoxyacetic acid (2,4-D). The catalysts produced were dominated by the tetragonal, crystalline anatase TiO₂ cell structure. The 0.05wt% Fe₂O₃-doped TiO₂ catalyst exhibited higher photocatalytic activity than that of undoped TiO₂ but its performance decline with increase Fe₂O₃ content due to possible increase of recombination centers. Photocatalytic degradation of 2,4-DA was optimized by response surface methodology. The highest 2,4-DA degradation (48%) was obtained when 1.0 g of 0.05wt% Fe₂O₃-doped TiO₂ is used to degrade 10 ppm of 2,4-DA at pH 4

Forecasting of global solar radiation using anfis and armax techniques

Procurement of measuring device, maintenance cost coupled with calibration of the instrument contributed to the difficulty in forecasting of global solar radiation in underdeveloped countries. Most of the available regressional and mathematical models do not capture well the behavior of the global solar radiation. This paper presents the comparison of Adaptive Neuro Fuzzy Inference System (ANFIS) and Autoregressive Moving Average with eXogenous term (ARMAX) in forecasting global solar radiation. Full-Scale (experimental) data of Nigerian metrological agency, Sultan Abubakar III international airport Sokoto was used to validate the models. The simulation results demonstrated that the ANFIS model having achieved MAPE of 5.34% outperformed the ARMAX model. The ANFIS could be a valuable tool for forecasting the global solar radiation

Bi-Template Assisted Sol-Gel Synthesis of Photocatalytically-Active Mesoporous Anatase TiO2 Nanoparticles

Sol-gel mesoporous titanium dioxide powders have been synthesized from chitosan and/or hexadecyltrimethylammonium bromide (HDTMA) and characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA) and N2 adsorption-desorption measurements. The photocatalytic performance of the synthesized meso-TiO2 powders was optimized based on the central composite design (CCD) of methyl orange (MO) degradation under UV light irradiation. The maximum MO degradation was 62.3% over a period of 60 min. Oxides produced using the binary chitosan and HDTMA template (C,H-TiO2) exhibited the relatively higher surface area (99.5 m2/g), smaller crystal size (12.78 nm), narrower band-gap energy (2.92 eV) and higher photocatalytic rate constant (0.0112 min–1) than as those from chitosan (C/TiO2) or HDTMA (H/TiO2) as the template

Influence of Side Chain on the Inhibition of Aluminium Corrosion in HCl by α-Amino Acids

Aside from functional groups, aromatic rings have mostly been regarded as zones via which certain inhibitors can protect etching metal parts. Substituent groups generally can be aromatic or non-aromatic, comparison of which is scanty in literature. Among these, amino acids exhibit side substituent chain in addition to amino- and carboxylic carbonyl- functional groups, hence may show unique behaviours in corrosive environment. The side chains of amino acids can vary from to H- to alkyl and then to aromatic. This study is devoted to the investigation of the influence of non-polar, hydrophobic side chain of amino acid homologues (glycine, alanine and phenylalanine) on the inhibition of aluminium corrosion in 0.3 M HCl. Corrosion properties and inhibition mechanism were analysed using mass loss, solid-state characterisation and quantum chemical methods. Potentiodynamic polarisation results confirmed cathodic inhibition, which was relatively less efficient with glycine and phenylalanine. The adsorption of these inhibitors was consistent with Langmuir isotherm and physical mechanism. Activation parameters, topography, electropotential shifts quantum studies and mass loss confirmed the superiority of the inhibiting effect of alanine. It is therefore argued herein that the aromatic carbocyclic moiety of phenylalanine does not dictate its anti-corrosion effect in acidic media, but preferentially, properties such as the adsorption type, corrosion medium, interfacial behaviour of adsorbates and temperature

Randomized controlled trial of fixed low-vs moderate-dose hydroxyurea for primary stroke prevention in Sub-Saharan Africa: Final results of the Spring Trial

Introduction: In children with sickle cell anemia (SCA) without transcranial Doppler (TCD) screening, the incidence rates of ischemic strokes is approximately the same among children living in low- and high- low-resource settings (Pediatr Neurol. 2019;95:73-78.) with a prevalence of ~ 11%. However, in high-income settings, the standard use of TCD ultrasonography, coupled initially with monthly blood transfusion therapy has dropped the stroke prevalence to < 1%. In a low-income setting, such as Nigeria, where 50% of children in the world with SCA are born (150,000 per year), initial monthly blood transfusion therapy is not practical for most children.In the Stroke Prevention in Nigeria (SPIN) Feasibility Trial (NCT01801423), fixed moderate-dose hydroxyurea was associated with a decreased rate of strokes in children with SCA and abnormal time-averaged mean of the maximum velocity (TAMMV) TCD measurements (≥200cm/sec) when compared to no treatment in the STOP Trial, 0.76 and 10.7 strokes per 100 person-years, repsectively (Am J Hematol. 2020). Based on the success of the SPIN trial, plus the challenges of real-world implementation of a government-supported primary stroke prevention programs for estimated 40,0000 children with SCA in three states in Nigeria, we tested the hypothesis that fixed-moderate dose (~20 mg/kg/day) hydroxyurea therapy for primary stroke prevention results in a 66% relative risk reduction (9 to 3 events per 100 person-years) when compared to fixed low-dose hydroxyurea (~10 mg/kg/day) therapy in a randomized controlled trial (The SPRING Trial; NCT02560935).Methods: In this partial-blind controlled phase III trial, we randomly assigned children between 5 and 12 years of age with SCA and a TCD time-averaged mean of the maximum velocity (TAMMV) ≥ 200 cm/sec measured independently twice or TAMMV ≥220 cm/sec once at study screening to receive fixed low-dose or fixed moderate-dose hydroxyurea. The primary endpoint was a clinical stroke or a transient ischemic attack (TIA). Myelosuppression was assessed with monthly complete blood counts (CBCs). Adherence to hydroxyurea was primarily based on an increase in MCV from baseline and monthly pill count return as a percent of dispensed pills. Hemoglobin F levels were measured at baseline, annually and upon trial exit. To evaluate the safety of hydroxyurea in the trial, children attending the same SCA clinics with TCD (TAMMV) <200 cm/sec at study screening were prospectively followed with biweekly phone calls and annual research visits.Results: A total of 220 children (mean age: 7.5 years, 51.8% female) were randomly assigned to fixed low- (10 mg/kg/day) or moderate- (20 mg/kg/day) dose hydroxyurea, and were followed for a median of 2.4 years (IQR 2.0-2.8). NINDS Clinical Trials leaders stopped the trial early because of futility for the primary outcome. In the fixed low- and moderate-dose hydroxyurea groups, the incidence rates of strokes per 100 person-years were 1.19 and 1.92 respectively, with an incidence rate ratio of 1.60 (95% CI: 0.31-10.34), p = 0.768. The incidence rate ratio of mortality when comparing the children treated with low- and moderate- fixed-dose hydroxyurea to the non-elevated TCD group (no hydroxyurea therapy, n= 211) was 1.97 (95% CI: 0.64-6.02) and 0.47 (95% CI: 0.05-2.38), p = 0.265 and 0.545, respectively. Returned pills during the trial was 5.4% and 4.8% in the fixed low- and moderate-dose groups, respectively, p= 0.144. MCV from baseline to endpoint increased 1.5fl and 7.2 fl in the fixed low- and moderate-dose groups, respectively, p<0.001. Upon exit from the trial 29.4% and 66.7% of the fixed- low and moderate -dose groups, respectively, had either hemoglobin level ≥ 9.0 g/dl, or a fetal hemoglobin level ≥ 20%.Conclusions: For primary stroke prevention in children with SCA, fixed low-dose, when compared to fixed moderate-dose hydroxyurea therapy, demonstrated no difference in the incidence rate of strokes. Both fixed low- and moderate -dose hydroxyurea doses are superior to no treatment for primary stroke prevention with abnormal TCD values. In partnership with Katsina, Kano, and Kaduna health department's leaders in Nigeria, 9 distinct SCA and primary stroke prevention clinics have been established, with the provision of free fixed low-dose hydroxyurea therapy (Bond Chemical, Nigeria; $0.15 per 500 mg) for abnormal TCD values, and biannual CBCs as standard care ,for over 40,000 children with SCA