The use of heavy metals in technological applications has led to detrimental effects on human health and the environment. Activated carbon and ion-exchange resins are commonly used to remove pollutants but they are expensive. Therefore, the research of low-cost alternatives derived from natural resources and organic wastes is being considered. The aim of this study considers the use of Calcium Alginate/Spent Coffee Grounds (CA-SCGs) composite beads to adsorb heavy metals from aqueous solutions, particularly, the removal of Ni 2+ or Cd 2+ at concentrations from 10 ppm to 100 ppm. CA-SCGs beads were made of equal proportions of alginate and spent coffee grounds and compared with calcium alginate beads (CA beads) and spent coffee grounds (SCGs) in terms of capacity and rate of adsorption. Three cycles of adsorption/desorption were done. The beads were characterized by Scanning Electron Microscopy coupled with an energy-dispersive X-ray spectroscopy (SEM-EDX), Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, and point of zero charge. Langmuir, Freundlich, and Sips models, and a pseudo-second-order kinetic equation were used. Sips model showed the best correlation with the adsorption of CA-SCGs beads with capacities of adsorption of 91.18 mg/g for cadmium and 20.96 mg/g for nickel. CA-SCGs beads had a greater adsorption than the CA beads, achieving adsorption percentages close to 100% than alginate alone, showing their effectiveness in heavy metal removal.
Calcium Alginate/Spent-Coffee-Grounds composite beads (CA-SCGs beads), which were made of two different proportions of alginate and spent-coffee-grounds (3:3 and 3:10), respectively, were used to adsorb Cu2+ in aqueous solution. These beads were compared with calcium alginate beads (CA beads) and spent-coffee-grounds (SCGs) in terms of adsorption capacity and rate of adsorption. The experiments were carried out at an initial pH of 4 at 30 °C with initial concentrations of Cu2+ from 10 ppm to 100 ppm. Equilibrium data was fitted with Langmuir, Freundlich and Sips models, and a pseudo-second-order kinetic equation. The Sips model showed the best correlation with the experimental values. CA-SCGs (3:3) beads showed a faster adsorption rate versus the CA beads. Also, CA-SCGs (3:3) beads showed a larger capacity of adsorption according to the Sips model, but not in the Langmuir model. FT-IR spectra and SEM images were taken for characterization. This study has shown that the CA-SCGs (3:3) beads have a synergistic effect, combining the capacity of adsorption of CA beads with the kinetics of the SCGs. The CA-SCGs beads have proven to be an effective adsorbent of Cu2+. Therefore, they can provide a use for the SCGs; which are considered pollutants in landfills.
The spectra of the fundamental and first and second overtones (Av = 1, 2, and 3) around the C-H stretch of ethylene in liquid argon solutions have been measured a t 88 K. The IR, near-IR, and visible spectra of pure liquid ethylene have been measured in the range from 2800 to 15 000 cm-I a t 109 K. Absorptions in the visible were obtained with a low-temperature cell and a resonant continuous wave laser technique with acoustic detection. Absorptions below 12 000 cm-I were observed at low temperatures with a Fourier transform spectrophotometer operating in the near-IR region. Comparison is made between the absorption bands of gas phase, liquid argon solution, and liquid phase ethylene. Spectra of solutions of ethylene in liquid argon show great simplification of the bands with respect to the room temperature gas-phase absorption bands. Due to the small frequency shift in solution, assignments are presented based on gas-phase measurements. For the C-H transitions of pure liquid ethylene, the local mode harmonic frequency and anharmonicity are obtained and used with a harmonically coupled anharmonic oscillator (HCAO) model to calculate the energy of the levels and assign the absorption bands to particular transitions.
A resonant optoacoustic technique is described using continuous wave laser excitation and piezoelectric detection of overtone absorptions of liquefied gases at cryogenic temperatures. This technique uses a piezoelectric detector directly attached to a low temperature cell inside a cryostat. The liquefied sample inside the cell is vibrationally excited in the visible region with a continuous wave dye laser. The laser is modulated around 100 kHz with an acousto-optic modulator. The modulation frequency corresponds to an acoustic resonance frequency of the cylindrical cell which increases the sensitivity of the detection system. The pressure wave detected by the piezoelectric transducer is sent to a lock-in amplifier and processed with a microcomputer. This sensitive technique is used to obtain the visible spectra of pure liquid methane and ethane. Spectra of the fourth overtone of the C-H stretch vibration of methane, in solution with liquid argon at 94 K, and in solution with liquid nitrogen at 84 K, are also reported. Comparison is made with nonresonant and pulsed acoustic techniques.
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