Preparation and application of metal ion-doped CoMgAl-hydrotalcite visible-light-driven photocatalyst

International Journal of Industrial Chemistry pp 1–11 | Cite as Preparation and application of metal ion-doped CoMgAl-hydrotalcite visible-light-driven photocatalyst AuthorsAuthors and affiliations Ali AuwaluTong LinlinShamsu AhmadYang HongyingJin ZhenanYan Song Open Access Research First Online: 11 April 2019 Abstract Preparation and application of CoMgAl-hydrotalcites have been studied. In this paper CoMgAl-LDHs photocatalysts were prepared by co-precipitation. Various techniques such as UV–visible spectrometry (UV–vis), BET, differential thermal gravimetric analysis, scanning electron microscopy analysis and X-ray diffraction were used to investigate the catalytic activity, structure, and composition of the prepared samples. The photocatalysts were developed as layered double hydroxides (LDHs) due to their layered structure with OH−. In the paper, specific surface area, thermal stability, absorption of visible light, and layered structure (crystal phase) were characterized by nitrogen adsorption–desorption method, differential thermal gravimetric analysis, UV–vis methods and X-rays diffraction. The results indicated that CoMgAl-LDHs caused photocatalytic degradation of methyl orange, rhodamine talcum, and methylene blue. Initially 1 g/L of the photocatalyst was used to degrade 40 mg/L of methyl orange, it was observed that 85.7% of the methyl orange was degraded at an illumination time of 300 min. However, the degradation of rhodamine and methylene blue was not good and did not give better results as that of methyl orange. KeywordsHydrotalcite Photocatalyst Absorption Degradation  Introduction Wastewater from dye industry has been considered as an important source of water pollution in the world due to its highly colored nature and refraction to degradation. Research on photocatalyst carried out in 1970s was commenced by irradiation of TiO2 photo-electrodes under irradiation of UV light and resulted in the decomposition of water to form oxygen and hydrogen [1, 2, 3]. Choi et al. investigated the photo reactivity of 21 metal ions that were doped into TiO2. It was found that when the metal ions were doped, they expanded TiO2 photo response into visible spectrum. However, when metal ions are added into TiO2, impurity and lattice energy levels were formed in the gap of TiO2. As represented in Eqs. 1 and 2 below. $${\text{M}}^{n + } + hv \to {\text{M}}^{{\left( {n + 1} \right) + }} + {\text{e}}^{ - }_{\text{ch}}$$ (1) $${\text{M}}^{n + } + \, hv \to {\text{M}}^{{\left( {n - 1} \right) + }} + \, hv^{ - }_{vb}$$ (2) where Mn+ & M are metal ion dopant and metal, respectively. The electron hole transfer between TiO2 and metal ion can alter the holes’ recombination as shown in Eqs. 3 and 4. $${\text{Hole trap:}} {\text{M}}^{n + } + \, h^{ + }_{vb} \to {\text{M}}^{{\left( {n - 1} \right) - }}$$ (3) $${\text{Electron trap: M}}^{n + } + {\text{ e}}^{ - }_{\text{cb}} \to {\text{M}}^{{\left( {n - 1} \right) + }}$$ (4) Furthermore, a main drawback of any powder form is that either the process has to be conducted in a suspension or the photocatalyst has to be immobilized on a carrier by compacting [4]. Mohsen et al. investigated in situ manganese doping of TiO2, single-step electrochemical anodizing titanium, such as Sulfur-dope TiO2, copper-decorated tungsten oxide-TiO2 nanotubes, iron-decorated tungsten-titania, tungsten-copper co-sensitized TiO2 nanotube composite photo anodes [5, 6, 7, 8]. Fe/WTNs photocatalytic activities were evaluated by degradation of aqueous Rhodamine B under xenon lamp radiation. It was discovered that the photocatalytic degradation reaction depends on many factors, such as the absorption of the dye on the catalyst surface, band gap energy, surface area, pore diameter, crystallinity, and electron–hole recombination rate [9, 10, 11, 12]. $$\left[ {{\text{M}}^{2 + }_{(1 - x)} {\text{M}}^{3 + }_{x} \left( {\text{OH}} \right)_{2} } \right]\left( {A_{x/n}^{n - } } \right).m{\text{H}}_{2} {\text{O}}$$ (5) where M2+ represents the divalent cations such as Mg2+, Fe2+, Ni2+, Cu2+, Co2+, Mn2+, Zn2+ or Cd2+, M3+ denotes the trivalent cations like Al3+, Cr3+, Ga3+ or Fe3+, An−, is the compensating anions (CO32−, SO42−, Cl−, NO3−, organic anions), An− is an interlayer n− valent anion and x varies between approximately 0.25 and 0.33 and m is the content of co intercalated-water [13, 14]. In the process of photocatalysis and fabrication, LDH-based photocatalysts are generally subjected to a variety of synthesis methods. However, some major challenges include simplifying the synthesis process with high crystallinity, high dispersion and adequate exposure of the active sites, precise control of particle size and morphology and long-term catalytic stability are encountered [15]. Various catalysts such as polyaniline Zr(IV) selenotungstophosphate nanocomposite (PANI/ZSWP nanocomposite) were prepared as a photocatalytic agent for dye degradation and as antimicrobial agent, such as the removal of harmful hazardous MB and MG dyes from water system and treatment of diseases causing pathogens [16]. A family of visible light-responsive Ni–Zn/Cr–CO32− ternary LDHs was synthesized by a co-precipitation method with varying the Ni/Zn atomic ratio. The study suggested that properly incorporating transition metals into the brucite layer of LDHs with suitable band edges might be a promising alternative for developing visible light-responsive ternary systems for hydrogen evolution [17]. Kulamani Parida et al. evaluated the photocatalytic activity via the photo-degradation of various colored and colorless pollutants under solar light, it was found that ZBHy4 LDH exhibited much higher photocatalytic activity than ZB4 LDH. The enhanced photocatalytic activity of ZBHy4 LDH is attributed to high crystallinity and phase purity, low recombination of charge carriers, long lifetime of photo-generated charges etc. [18]. The thermal stability of Cu–Cr LDH increased by increasing Co amount in the brucite layer and photocatalyst exhibits high photocatalytic activity in the visible region due to the cooperative effect of binary cations and more electron-transfer capability of cobalt along with uniform pore size distribution [19]. OG/La2O3/ZrO2 nanocomposite has been fabricated by co-precipitation method. OG sheets provided high surface area for the adsorption of dyes to take place and the deposition of other two metal oxides onto the OG helped in suppressing the electron–hole pair recombination ability thus, leading to high photocatalytic activity of OG/La2O3/ZrO2 towards the degradation of fast green dye [20]. The photocatalytic activity of ChPA/ZS nanocomposite was measured by the photo-degradation of Congo red and methyl orange dyes under solar light radiations and the results indicated that chitosan-g-poly(acrylamide)/ZnS nanocomposite had an ability for dye removal under simultaneous adsorption and photo-degradation [21]. A novel PAM/NZP nanocomposit (...truncated)