br Experimental procedure br Results br Discussion br Conclusions

Experimental procedure

Results

Discussion

Conclusions
Joining of bare alumina ceramic/Cu was carried out in air through an ultrasonic-assisted brazing method by using a Zn-14Al filler metal for a serial UVDT. The effects of the UVDT on the microstructures and mechanical properties of the joints were systematically investigated. The conclusions were summarized as follows:

Introduction
One of the major concerns in the developing countries is the presence of organic dyes in wastewater of several industries such as textile, paper, leather and food processing. The organic dyes cause serious problems for human health and other living organisms because of their toxic and carcinogenic effects [1,2]. In light of this, elimination of industrial organic dyes from wastewater has gained great attention. The treatment of polluted wastewater containing organic dyes can be performed with different physicochemical and biological methods including adsorption, chemical oxidation, membrane technology and advanced oxidation processes (AOPs) [3–5]. Adsorption is one of the most effective treatment processes due to its simplicity and low cost [6]. Various materials have been used for dye removal from wastewater via adsorption. Recently, carbon based adsorbents have been frequently used in water purification due to their abundance and low cost [7]. Hydrochar is a carbon-based adsorbent prepared through hydrothermal carbonization of SAG supplier wastes, such as spent coffee grounds or rice husk [8,9]. However, it is difficult to separate the used carbon-based adsorbents from treated wastewater. For this, Fe3O4-loaded adsorbents have attracted great attention due to their unique properties such as easy recovery through a magnet, large surface area, simple manipulation process and high separation efficiency [10–12].
Another technique to enhance the efficiency of adsorption technique is the combination with other treatment processes [6,13]. Ultrasounds have been used frequently in direct degradation of organic pollutants or in combination with catalysts or adsorbents in ultrasound-assisted processes [14,15]. The improved removal efficiency of pollutants in ultrasound-assisted processes can be explained through the following mechanisms: (i) Direct sonolysis of pollutants: high intensity ultrasonic waves in liquid phase produce bubbles in liquid medium by cavitation phenomena. Collapsing of these bubbles generates localized high temperature and pressure, which in turn convert H2O molecules to OH and H radicals. The produced OH radicals attack and degrade the organic pollutants [16,17]. (ii) Sonocatalysis: the presence of suitable particles can enhance the oxidation efficiency of the system by generating more nucleation sites for cavitation phenomena [17,18]. (iii) Ultrasound-assisted enhanced adsorption: the resulted energy from ultrasonic irradiation enhances the mass transfer efficiency through convection pathway and also activates the surfaces sites of aggregated particles [6,7]. Furthermore, it has been proven that ultrasonic irradiation can be used as a very effective technique in increasing the adsorption of dyes on adsorbent by enhancing the affinity between adsorbent and adsorbate.
In this study, Fe3O4-loaded coffee waste hydrochar (Fe3O4-CHC) was synthesized through a simple precipitation method. The synthesized adsorbent was characterized by SEM, TEM, EDX, XRD, BET and FT-IR analysis. The ultrasound-assisted process in the presence of Fe3O4-CHC was used to remove AR17 dye from aqueous solution. The effects of adsorbent dosage, initial dye concentration, presence of inorganic anions and ultrasonic power on the dye removal efficiency were investigated. The Langmuir and Freundlich isotherms were used to justify the experimental data. The produced intermediates of degradation of AR17 were also identified by GC–MS analysis.

Materials and methods

Results and discussion

Conclusions
The Fe3O4-loaded coffee waste hydrochar (Fe3O4-CHC) was synthesized using a simple precipitation method. The results of SEM, TEM, EDAX, XRD, BET and FT-IR analysis confirmed the formation of Fe3O4 nanoparticles on the surface of the hydrochar. The results of BET analysis showed that the specific surface area increased from 17.2 to 34.7m2/g after loading Fe3O4 onto the bare hydrochar. The synthesized Fe3O4-CHC was used for removal of AR17 anionic dye through ultrasound-assisted adsorption process. An increase in Fe3O4-CHC dosage up to 2g/L led to the enhancement in the removal efficiency of AR17. With increasing initial dye concentration, the removal efficiency decreased from 100 to 74%. The presence of Cl− and SO42− ions retarded the removal of AR17. The results of the reusability tests showed that Fe3O4-CHC adsorbent can be used effectively for several runs for organic pollutants removal. The high correlation coefficient (R2=0.997) obtained from the Langmuir model indicated that physical and monolayer adsorption of dye molecules occurred on the Fe3O4-CHC surface.