Comparison of discharge characteristics and methylene blue degradation through a direct-current excited plasma jet with air and oxygen used as working gases

Through using a direct-current driven plasma jet operated underwater,degradation of methylene blue(MB)is investigated with air and oxygen used as working gases.With a low power voltage,a plasma plume extends from the needle electrode,which is purple in air.It turns pink after it bridges the two electrodes.During the process,oxygen plasma remains white.Discharge operates in a pulsed mode or a continuous one,which depends on the magnitude of power voltage.For the pulsed mode,oxygen discharge has a shorter plume and a higher pulse frequency than air discharge under the same power voltage.For the same current of the continuous mode,both power and gap voltages of oxygen discharge are higher than those of air discharge.Moreover,MB degradation efficiency increases with increasing power voltage or initial concentration of MB solution.Compared with air discharge,oxygen discharge has a higher degradation efficiency with the same power voltage and treatment time.The pulsed oxygen discharge with power voltage of about 6.5 k V has the highest efficiency in degrading MB dye,reaching approximately 85.8%after 10 min treatment.As a comparison,after 10 min treatment in air discharge,the highest degradation efficiency is 63.7%,which appears in the continuous mode at a power voltage of 10.6 kV.Besides,optical spectra from the discharges are also compared for the two types of working gases.

Graphene-wrapped Ag3PO4/LaCO3OH heterostructures for water purification under visible light

We demonstrated a unique synthesis approach of graphene（GR）-wrapped AgPO/LaCOOH（APO/LCO）heterostructures by an in-situ wet chemical method. FESEM analysis reveals the formation of rhombic dodecahedrons of APO decorated with LCO and later wrapped with GR flakes. Optical studies shows two absorption edges corresponding to the band gap energies of APO（2.41 eV） and LCO（4.1 eV）. Considering the absorption edge of the heterostructures in the visible region, the photocatalytic activities of photocatalysts containing different APO/LCO mass ratios were evaluated by the degradation of MB. GR-decorated composite with 20% LCO（APO/LCO20/GR） exhibited the highest photocatalytic activity for MB degradation, with a rate constant, k of 0.541 min. The photocatalytic activity of APO/LCO20/GR more greatly enhanced than those of the individual constituents（APO, LCO, APO/LCO20）. The enhanced photocatalytic activity of the heterostructure can be attributed to the co-catalytic effect of LCO as well as intriguing physicochemical properties of GR. To understand the enhanced photocatalytic activity of the heterostructures the photocatalytic reaction mechanism is proposed in detail. The recyclability of the APO/LCO/GR composite photocatalyst is further evaluated by reusing the catalyst in replicate photocatalytic experiments which shows consistent photocatalytic activity thereby confirms the stability and reusability of heterostructure photocatalyst.

Green synthesis of magnetically separable and reusable Fe_(3)O_(4)/Cdots nanocomposites photocatalyst utilizing Moringa oleifera extract and watermelon peel for rapid dye degradation

This study focused on green-synthesized magnetite/carbon dots nanocomposites(GS-Fe_(3)O_(4)/Cdots)utilizing Moringa oleifera leaf extract and watermelon peel waste for rapid degradation of methylene blue(MB)dye.Co-precipitation and hydrothermal method were used to synthesize GS-Fe_(3)O_(4) and Cdots,respectively.In addition,the sonication method was used to link Cdots on Fe_(3)O_(4) surface.X-ray diffraction spectrum of GS-Fe_(3)O_(4)/Cdots inform the cubic inverse spinel and has crystallite size in the range of 10.1-7.2 nm.The crystallite size also decreased with the increase of Cdots concentration.The transmission electron microscope showed the most uniform size of nanocomposites at around 13.4 nm.The functional group of Fe-O was detected on the nanocomposites,proof that Fe_(3)O_(4) still exists after fabrication.The presence of C=C,C-O,and C-O-C also indicates the existence of Cdots on the surface of Fe_(3)O_(4).The addition of Cdots affected the saturation magnetization and coercivity value in the range of 29.2-38.3 emu/g and 59-65 Oe,respectively,which showed a good magnetic properties.As an organic dye,MB was used for a photocatalytic process under UV irradiation.The degradation efficiency was raised to 98% for 30 min photocatalytic process.The magnetically separable capability makes nanocomposites could be recycled and reused three times with high degradation.Furthermore,GS-Fe_(3)O_(4)/Cdots potential as a low-cost and environmentally friendly reusable photocatalyst for rapid wastewater degradation.