Photocatalytic and Adsorption Performances of Faceted Cuprous Oxide (Cu2O) Particles for the Removal of Methyl Orange (MO) from Aqueous Media.

Particles of sub-micron size possess significant capacity to adsorb organic molecules from aqueous media. Semiconductor photocatalysts in particle form could potentially be utilized for dye removal through either physical adsorption or photo-induced chemical process. The photocatalytic and adsorption capabilities of Cu2O particles with various exposed crystal facets have been studied through separate adsorption capacity test and photocatalytic degradation test. These crystals display unique cubic, octahedral, rhombic dodecahedral, and truncated polyhedral shapes due to specifically exposed crystal facet(s). For comparison, Cu2O particles with no clear exposed facets were also prepared. The current work confirms that the surface charge critically affects the adsorption performance of the synthesized Cu2O particles. The octahedral shaped Cu2O particles, with exposed {111} facets, possess the best adsorption capability of methyl orange (MO) dye due to the strongest positive surface charge among the different types of particles. In addition, we also found that the adsorption of MO follows the Langmuir monolayer mechanism. The octahedral particles also performed the best in photocatalytic dye degradation of MO under visible light irradiation because of the assistance from dye absorption. On top of the photocatalytic study, the stability of these Cu2O particles during the photocatalytic processes was also investigated. Cu(OH)2 and CuO are the likely corrosion products found on the particle surface after the photocorrosion in MO solution. By adding hole scavengers in the solution, the photocorrosion of Cu2O was greatly reduced. This observation confirms that the photocatalytically generated holes were responsible for the photocorrosion of Cu2O.

Enhanced photocatalytic activity of green synthesized zinc oxide nanoparticles using low-cost plant extracts.

Developing stable and highly efficient metal oxide photocatalysts remains a significant challenge in managing organic pollutants. In this study, zinc oxide nanoparticles (ZnO NPs) were successfully synthesized using various plant extracts, pomegranate (P.M), beetroot roots (B.S), and seder, along with a chemical process. The produced ZnO NPs were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-Vis), Field Emission Scanning Electron Microscope (FESEM), High-Resolution Transmission Electron Microscopy (HRTEM), and Surface Area. For all prepared samples, the results indicated that the composition of the plant extract affects several characteristics of the produced particles, such as their photocatalytic properties, energy bandgap (Eg), particle size, and the ratio of the two intensity (0 0 2) and (1 0 0) crystalline planes. The particle size of the produced NPs varies between 20 and 30 nm. To examine NPs' photocatalytic activity in the presence of UV light, Methyl Orange (MO) was utilized. The Eg of  ZnO synthesized by the chemical method was 3.16 e. V, whereas it was 2.84, 2.63, and 2.59 for P.M, Seder, and B.S extracts, respectively. The most effective ZnO NPs, synthesized using Beetroots, exhibited a degradation efficiency of 87 ± 0.5% with a kinetic rate constant of 0.007 min-1. The ratio of the two intensity (0 0 2) and (1 0 0) crystalline planes was also examined to determine a specific orientation in (0 0 2) that is linked to the production of oxygen vacancies in ZnO, which enhances their photocatalytic efficiency. Furthermore, the increase in photocatalytic effectiveness can be attributed to the improved light absorption by the inter-band gap states and effective charge transfer.

Novel GdTaO4 phase for efficient photocatalytic degradation of organic dye under visible light irradiation: An X-ray spectroscopic investigation.

The novel GdTaO4 phase exhibits good photocatalytic activity under visible light irradiation and holds great promise for the removal of organic dyes from industrial wastes. The GdTaO4 samples were synthesized using the hydrothermal and calcination process with different weight ratios of gadolinium nitrate hydrate (G) and tantalum pentachloride (T), and their structural studies confirmed the formation of the GdTaO4 (GT) phase. Among the samples, GT-4 (with a weight ratio of 4:1) exhibited the highest photocatalytic activity for the degradation of Methyl Orange (MO) dye under visible light irradiation. To enhance the photocatalytic performance, H2O2 was used as a green additive, and the photocatalytic abilities were examined by varying dye types and concentrations. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) revealed the local atomic and electronic structures around Ta and Gd and highlighted the contribution of Gd3+ to the GT system, which is a crucial factor in supporting the enhanced photocatalytic performance. Moreover, in-situ XAS at Gd M5-edge and O K-edge were examined under illumination/dark conditions to explore the electronic structures of photo-excited electron transition in the photocatalytic process. The analytical results provided strong evidence correlating the electronic structure and photocatalytic property of the GT. This study demonstrates that GdTaO4 exhibits good photocatalytic activity under visible light irradiation, making it a promising new Ta-based photocatalyst for the effective removal of organic dyes from industrial wastes.

Preparation and Photodegradation Properties of Carbon-Nanofiber-Based Catalysts.

In this study, an iron oxide/carbon nanofibers (Fe2O3/CNFs) composite was prepared by a combination of electrospinning and hydrothermal methods. The characterization of Fe2O3/CNFs was achieved via scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It is shown that when the hydrothermal reaction time was 180 °C and the reaction time was 1 h, the Fe2O3 nanoparticle size was about 90 nm with uniform distribution. The photodegradation performance applied to decolorize methyl orange (MO) was investigated by forming a heterogeneous Fenton catalytic system with hydrogen peroxide. The reaction conditions for the degradation of MO were optimized with the decolorization rate up to more than 99% within 1 h, which can decompose the dyes in water effectively. The degradation process of MO by Fenton oxidation was analyzed by a UV-visible NIR spectrophotometer, and the reaction mechanism was speculated as well.

[Preparation of melamine-functionalized porous organic polymer and its adsorption properties for methyl orange].

In this work, a polymer precursor was first synthesized using p-terphenyl (TP) and terephthaloyl chloride (TC) as monomers. Then, cross-linking was realized by means of a Schiff base reaction with melamine (MA) as a modifier to obtain an amine-functionalized porous organic polymer TP-TC-MA. The synthesized polymers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), and point of zero charge (pHpzc) measurements, as well as on the basis of nitrogen adsorption-desorption isotherms. Adsorption experiments were carried out to evaluate the adsorption properties of TP-TC-MA for methyl orange (MO), a typical anionic azo dye that has widespread industrial application. The amount of MO adsorbed on TP-TC-MA was evaluated by ultraviolet-visible (UV-Vis) spectroscopy at a wavelength of 463 nm. Microscopic analysis revealed that the as-synthesized polymer had an aggregated particle-shaped structure. XRD spectra confirmed that TP-TC-MA was an amorphous polymer, consistent with the results of high-resolution TEM experiments. The Brunauer-Emmett-Teller (BET) specific surface area and total pore volume of TP-TC-MA were determined as 708.5 m 2/g and 0.556 cm3/g, respectively. The measured pHpzc of TP-TC-MA was 4.0, probably because of the abundant nitrogen-containing groups provided by MA. The factors affecting adsorption, such as pH, adsorbent dosage, contact time, initial pollutant concentration, and ionic strength, were investigated. Because of the protonation of the N-atom in TP-TC-MA, the pH had a strong impact on the adsorption of MO. The removal efficiency could be maximized at the optimized pH of 3.0. The adsorption equilibrium isotherm, measured at 25 ℃ and a concentration of 50-500 mg/L, showed that the MO adsorption over TP-TC-MA followed the Langmuir isotherm, with a maximum adsorption capacity of 156.3 mg/g. The modeling of the experimental adsorption data was consistent with the pseudo-second-order kinetic model, which indicated fast adsorption and chemisorption as the dominant mechanism. With increasing ionic strength, the adsorption of MO slightly decreased, suggesting a partial antagonistic ion effect. Results of the selectivity study revealed that TP-TC-MA was more selective toward MO than methylene blue (MB), which indicated that electrostatic interactions played a significant role during the adsorption progress. Five adsorption-desorption cycles showed that TP-TC-MA could be regenerated without significant deterioration of its adsorption efficiency, indicating that it has good stability and reusability. The observed adsorption performance indicated that this MA-modified porous organic polymer offers prospects for further research and application in the treatment of dye-containing wastewaters.

Energizing periodic mesoporous organosilica (PMOS) with bismuth and cerium for photo-degrading methylene blue and methyl orange in water.

This work reported an efficient catalyst to reduce the organic pollutants by using an energetic periodic mesoporous organosilica (PMOS) supported with bismuth (Bi-PMOS) and cerium (Ce-PMOS). PMOS support was designed through co-condensation of sodium silicate and 3-methacryloxypropyltrimethoxysilane on polysorbate templates. The resultant PMOSs were fabricated with bismuth and cerium oxides to formulate Bi-PMOS and Ce-PMOS, respectively. These materials showed photo-degradations of methylene blue (MB, 74.7% and 41.1% with Bi-PMOS and Ce-PMOS, respectively) and methyl orange (MO, 53.2% and 39.4% with Bi-PMOS and Ce-PMOS, respectively). Such efficient photo-degradations were attributed to the precise doping of metallic nodes of Bi2 O3 and CeO2 on the porous structure of PMOS with high surface area. The results also showed that Bi and Ce were more effective in PMOS support for photo-degradation of dyes as the support provides more lifetime to photo-generated electron-hole pairs than other materials. Moreover, active reusability and high degradation efficiencies of Bi-PMOS and Ce-PMOS proved them better analytical tools to reduce organic pollutants under visible lights. PRACTITIONER POINTS: The oxides of bismuth and cerium have impressive photocatalytic characteristics. New material energizing mesoporous organosilica with bismuth and cerium for photo-degradation of methylene blue and methyl orange in water. The use of an efficient catalyst to reduce the organic pollutants by using an energetic periodic mesoporous organosilica (PMOS) supported with bismuth (Bi-PMOS) and cerium (Ce-PMOS).

Enhanced adsorption properties of organic ZnCr-LDH synthesized by soft template method for anionic dyes.

Organic ZnCr-LDH (ST-LDH) was synthesized by a facile one-step hydrothermal technique using methyl orange (MO) as a soft template agent, which can efficiently remove methyl orange (MO), Congo red (CR), and orange II (OII) from aqueous solution. The microstructure of ST-LDH by modifying changed obviously, from the cellular structure to the stacking structure formed by the face-face contact of hydrotalcite nanosheets, which resulted in much more exchangeable nitrate ions to remain in the interlayer space. The pre-insertion of benzene sulfonate as a pillar expanded the interlayer gallery, which facilitated the pollutant anions (MO, CR, and OII) into the interlayer of LDH in the subsequent adsorption process. The maximum adsorption capacity of ST-LDH for MO, CR, and OII was 4200.8 mg/g, 1252.0 mg/g, and 1670.6 mg/g, respectively, which is approximately 1.86 times, 1.8 times, and 2.32 times that of the pristine NO3-LDH, respectively. The removal mechanism of anionic dyes was determined as anion exchange between NO3- anions and dye molecules. The adsorption behavior for MO and OII is multilayer adsorption, while the adsorption behavior for CR is monolayer adsorption. The adsorption process mainly was controlled by the chemical bonding between the dye molecules and adsorbent active sites. The LDH can be effectively regenerated by photocatalysis after MO adsorption. The ST-LDH has a great potential to be used as a high-efficient adsorbent to remove anionic dyes from aqueous solution. The schematic illustration of the synthetic process of soft template agent modified and unmodified hydrotalcites by one-pot hydrothermal method and the adsorption process of MO by ST-LDH were shown in Fig. 12. Modified hydrotalcite (ST-LDH) was prepared using methyl orange (MO) as a soft template agent. Compared with unmodified hydrotalcite (NO3-LDH), the insertion of benzene sulfonate anions into the hydrotalcite layer resulted in the increase of the interlayer spacing from 8.269 to 8.654Å. The LDH host structure pre-intercalated by benzene sulfonate anions evolved into pillared materials in interlayer; benzene sulfonate anions as a column expanded the interlayer spacing of (003) base plane, which facilitated the pollutant anions (MO, CR, and OII) into the interlayer of ST-LDH and exchanged with NO3- anion in the subsequent adsorption process. It can be inferred that in the process of modification hydrotalcite by benzene sulfonate, a small amount of benzene sulfonate anions pre-inserted into the gallery of hydrotalcite with a monolayer model in the process of hydrotalcite modification, and its inclination angle is calculated to be about 29.1°. After ST-LDH sample adsorbed the MO molecules, dye molecules intercalated into the LDH host, and successful exchange with NO3- anions, the d003 value increased to 24.78 Å. A large amount of MO- anions were intercalated into the gallery of ST-LDH with a bilayer model according to the Freundlich isotherm model, and the tilting angle increases to 53.6°. The adsorption capacity of MO by ST-LDH was significantly enhanced to 4200.8 mg/g, which was much higher than that of NO3-LDH (2252.8 mg/g). Schematic illustration of the synthetic process of LDH materials and adsorption process of MO by ST-LDH.

[Effects and Mechanisms of Methyl Orange Removal from Aqueous Solutions by Modified Rice Shell Biochar].

Waste rice shell (RS) was used for modified biochar preparation via different activation methods. The types of modifiers, impregnation ratio, and pyrolysis temperature have significant effects on the characteristics of biochar and the adsorption capacity of methyl orange (MO). The physical and chemical properties of modified biochar and MO adsorption mechanisms were analyzed by N2-adsorption, X-ray diffraction (XRD), Fourier infrared spectroscopy (FT-IR), field emission scanning electron microscopy (SEM), thermogravimetric analyzer (TG), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) techniques. The results showed that the modified biochar (named Z2RT400) prepared at 400℃ with a mass ratio of 2:1 (ZnCl2:rice shell) had the highest adsorption capacity for MO. Under the following conditions with a solution pH value of 4, adsorbent dosage of 10 mg, initial MO concentration of 2000 mg·L-1, and reaction time of 420 min, the maximum adsorption capacity of Z2RT400 was 1967.72 mg·g-1. When the adsorbent dosage was 80 mg, the maximum removal rate reached 99.52%. The adsorption data fitted well with the pseudo-second order kinetic model and Freundlich isotherm model, which indicates that chemical adsorption is the main adsorption mechanism and physical adsorption is the auxiliary adsorption mechanism. Therefore, the waste rice shell derived biochar can be used as a highly efficient dye adsorbent in applications such as sewage treatment.

High performance NiFe layered double hydroxide for methyl orange dye and Cr(VI) adsorption.

The NiFe layered double hydroxides (LDHs) with different mole ratio of Ni/Fe (4:1, 3:1, 7:3 and 1:1) were prepared by a simple coprecipitation method. The adsorption performance were evaluated by the removal of methyl orange (MO) dye and hexavalent chromium(VI) heavy metal ion. It is found that Ni4Fe1-LDH can remove more than 92% of MO in 10 min at the 10 mg/L MO initial concentration, and 97% of Cr(VI) in 1 h at 4 mg/L Cr2O7(2-) initial concentration. The saturated adsorption capacity of Ni4Fe1-LDH is found to be as large as 205.76 mg/g for MO and 26.78 mg/g for Cr(VI). The adsorption behavior of this new adsorbent is fitted well with Langmuir isotherm and the pseudo-second-order kinetic model, indicative of a monolayer and chemical adsorption that synergistically originates from exchangeable anions mechanism and layer charge density. Due to the excellent removal capacity of MO and Cr(VI), the NiFe-LDHs could be a promising adsorbent for wastewater treatment.

[Preparation of Visible-light-induced g-C3N4/Bi2S3 Photocatalysts for the Efficient Degradation of Methyl Orange].

Visible light responsive heterojunctions of graphitic carbon nitride (g-C3N4) and Bi2S3 were successfully designed and constructed by a simple solvothermal process. The as-prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and UV-vis diffuse reflectance spectroscopy (DRS). Under visible light irradiation, the as-prepared g-C3N4/Bi2S3 photocatalysts exhibited highly enhanced photochemical efficiency in the degradation of methyl orange (MO) compared with pure g-C3N4 and Bi2S3. On the basis of the calculated energy bands, the excellent enhancement was attributed to the efficient separation of photoinduced electron-hole pairs. In addition, a detailed degradation pathway of MO degradation by g-C3N4/Bi2S3 composites was proposed to further elucidate the inner photodegradation mechanism. This research may provide a cost-effective and easy-scaling up approach to develop visible-light-driven photocatalysts, which could be applied in wastewater treatment.

Facile synthesis of high photocatalytic active porous g-C3N4 with ZnCl2 template.

Zinc chloride was utilized as the multi-functional modifier with dicyandiamide to synthesize porous g-C3N4, it not only played the role of pore-former in the resulting composite, but also acted as the assistant in succeeding adsorption of methyl orange (MO). Adjusting the quantity of ZnCl2 additive combined with the concentration of acidic washing liquid could control the amount and distribution of residual zinc species in the g-C3N4, in order to enhance the activity of the photocatalyst. The resulting composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis diffuse reflection spectroscopy (UV-vis) and X-ray photoelectron spectroscopy (XPS) as well as photoluminescence (PL) to assess the influence of residual zinc species on the physical and optical property of the composite. And they were evaluated in the photocatalytic degradation of MO in the visible light region, exhibiting an activity 240% higher than that of g-C3N4.

Removal of methyl orange from aqueous solutions through adsorption by calcium aluminate hydrates.

Methyl orange (MO) is a kind of anionic dye and widely used in industry. In this study, tricalcium aluminate hydrates (Ca-Al-LDHs) are used as an adsorbent to remove methyl orange (MO) from aqueous solutions. The resulting products were studied by X-ray diffraction (XRD), infrared spectroscopy (MIR), thermal analysis (TG-DTA) and scanning electron microscope (SEM). The XRD results indicated that the MO molecules were successfully intercalated into the tricalcium aluminate hydrates, with the basal spacing of Ca-Al-LDH expanding to 2.48 nm. The MIR spectrum for CaAl-MO-LDH shows obvious bands assigned to the N=N, N=H stretching vibrations and S=O, SO3(-) group respectively, which are considered as marks to assess MO(-) ion intercalation into the interlayers of LDH. The overall morphology of CaAl-MO-LDH displayed a "honey-comb" like structure, with the adjacent layers expanded.

Microporous spongy chitosan monoliths doped with graphene oxide as highly effective adsorbent for methyl orange and copper nitrate (Cu(NO3)2) ions.

In the current study, microporous spongy chitosan monoliths doped with small amount of graphene oxide (CSGO monoliths) with high porosity (96-98%), extraordinary high water absorption (more than 2000%) and low density (0.0436-0.0607 g cm(-3)) were prepared by the freeze-drying method and used as adsorbents for anionic dyes methyl orange (MO) and Cu(2+) ions. The adsorption behavior of the CSGO monoliths and influencing factors such as pH value, graphene oxide (GO) content, concentration of pollutants as well as adsorption kinetics were studied. Specifically, the saturated adsorption capacity for MO is 567.07 mg g(-1), the highest comparing with other publication results, and it is 53.69 mg g(-1) for Cu(2+) ions. Since they are biodegradable, non-toxic, efficient, low-cost and easy to prepare, we believe that these microporous spongy CSGO monoliths will be the promising candidates for water purification.