Carbon might be the most widely-used material in sensor applications. It has the combined properties of a porous surface, electrical conductivity, biocompatibility, and chemical and electrochemical stability [1,2]. Many studies have shown that the electrical properties of carbon nano- or micro-sized materials as a sensor electrode have the ability to efficiently sense surface changes [3,4,5,6]. The integration of carbon nanomaterial into electrodes has been challenging due to cost and toxicity issues [7,8,9]. On the contrary biomass products like coffee waste is a qualified carbon raw material for the synthesis of valuable carbon materials because it is available in high quality and huge amounts, and it is an environmentally friendly renewable resource [10]. Coffee is one of the most important commodities and widely consumed beverages all around the world and grown in about 80 countries [11]. The global production has reached 11–13 million tons [12,13]. It is estimated that only in Italy more than 14 billion expressos are consumed every year and the number is growing continuously [14]. There are many ways to distinguish coffee such as origin, botanical variety, growing conditions, physiology, flavour, roasting, pre- and post-processing etc. [15]. The chemical composition (more than 1000 chemicals) [16] of coffee depends on physiological aspects such as degree of maturation [17,18,19]. Complex reactions take place during roasting at high temperatures and modify considerably coffee’s chemical composition, with some beneficial compounds are degraded and some others created. More than 950 compounds have been identified after roasting [20]. On the other hand, an estimated 380,000 tons of brewed coffee waste is discarded each year [16]. The pollution caused by coffee waste has also been a concern due to the high content of organic matter like caffeine, free phenols and tannins (polyphenols), and acid content, which are known to be very toxic to many life processes [21]. Coffee waste constitutes a source of a serious environmental problems in coffee-using countries [22]. There has been a significant amount of research activity going on in the area of waste coffee and its by-products utilisation during the last years. Numerous studies on the use of coffee waste lead to the conclusion that coffee by-products and wastes can be used in a variety of ways [23]. Most of the work is directed towards the use of this waste as starting material for the production of bioactive compounds, antioxidants, food additives, feeds, beverages, vinegar, biogas, caffeine, pectin, pectic enzymes, protein, and compost [24,25,26]. Previous studies have confirmed that the presence of toxic materials can be minimized by extracting them with hot water brewing. Coffee waste residue is practically pure lignocellulose [27]. Consequently, scientists no longer consider these residues as a waste, but rather as a raw material for other processes [28]. Considering the literature and waste brewed coffee powder (WBCP) availability in massive amounts, WBCP is a qualified raw material as a carbon material source for environmentally friendly treatments like pyrolysis [5,10]. The presented work demonstrated the applicability of a ‘best from waste’ approach. It can close the loop of brewed coffee waste by leading to a new porous carbon-based product. The porous surface of carbonized coffee waste is a unique property suitable for its high surface activity [29]. Thus, in this research, carbon from waste coffee was targeted and tested as a relative humidity sensor for industrial and household applications [30,31,32]. It has been found that the porous films exhibit higher humidity sensitivity than the nonporous counterparts [33]. The presence of inter/intragranular porosity and pore size distribution are influential factors for humidity sensors [34,35]. In this work the humidity sensing characteristics of pyrolyzed coffee waste-based sensors were investigated at room temperature in a relative humidity (RH) range from 0 up to 98%.

Mengatasi Krisis Cyanobacteria dengan Biochar: Inovasi untuk Masa Depan Air Bersih

Kekurangan sumber daya air merupakan ancaman serius bagi kehidupan modern, dengan ledakan cyanobacteria di danau dan waduk yang semakin sering terjadi dalam beberapa tahun terakhir. Ketika jumlah sel cyanobacteria meningkat secara signifikan di permukaan air, tantangan dalam pengolahan air minum pun semakin besar. Tambahan lagi, materi organik alga (AOM) yang dihasilkan oleh cyanobacteria, seperti toksin alga dan zat penghasil bau, dapat menghasilkan produk sampingan disinfeksi yang berpotensi membahayakan kesehatan manusia. Oleh karena itu, menjaga air minum bebas dari cyanobacteria dan AOM adalah suatu keharusan yang mendesak.

Untuk menanggapi tantangan ini, pendekatan oksidasi pra-kimia sering digunakan untuk meningkatkan efisiensi koagulasi dalam penghilangan cyanobacteria. Salah satu metode yang telah dianggap adalah menggunakan TiO2 sebagai fotokatalis, yang menghasilkan radikal untuk oksidasi pra-kimia dan meningkatkan efisiensi koagulasi, sehingga dosis koagulan dapat dikurangi. Namun, penggunaan nanopartikel TiO2 dalam jumlah yang berlebihan dapat berpotensi merugikan lingkungan dan kesehatan manusia.

Sebagai solusi alternatif, penggunaan biochar (BC) sebagai substrat telah menarik perhatian. BC, yang berasal dari berbagai sumber biomassa seperti limbah organik dan sisa tanaman, adalah bahan berbasis karbon yang melimpah dan ramah lingkungan. Penggunaannya sebagai substrat dapat meningkatkan kinerja katalitik TiO2, menghasilkan efisiensi oksidasi yang lebih tinggi dan memungkinkan pengurangan dosis TiO2 yang diperlukan untuk menjaga keamanan lingkungan. Studi telah menunjukkan bahwa komposit TiO2/biochar dapat meningkatkan efisiensi kavitasi ultrasonik dan mendegradasi senyawa organik, berkat jumlah pusat aktif yang besar yang mempromosikan transfer massa molekul reaktan ke permukaan katalis.

Dalam konteks ini, penelitian telah mengeksplorasi potensi kombinasi ultrasonik dan TiO2/biochar untuk menghilangkan cyanobacteria melalui proses koagulasi-pelarutan. Dengan menggunakan Microcystis aeruginosa sebagai model cyanobacteria, penelitian tersebut bertujuan untuk mensintesis nanokomposit TiO2 yang dimuat BC dan mengevaluasi efektivitasnya dalam menghilangkan cyanobacteria. Selain itu, kualitas air setelah perlakuan, termasuk konsentrasi toksin alga dan karbon organik terlarut, serta populasi cyanobacteria utuh setelah perlakuan, juga dianalisis.

Hasil penelitian menjanjikan dan menunjukkan bahwa pendekatan ini memiliki potensi untuk menjadi proses pra-oksidasi yang efektif dalam pengolahan air minum, dengan mempertimbangkan kedua efisiensi penghilangan cyanobacteria dan keamanan air minum. Selain itu, penggunaan biochar sebagai substrat menawarkan solusi yang ramah lingkungan dan berkelanjutan, menunjukkan bahwa inovasi dalam bidang pengolahan air dapat menyatukan kebutuhan akan air bersih dengan kepedulian terhadap lingkungan. Dengan terus mengembangkan dan menerapkan teknologi ini, kita dapat menciptakan masa depan yang lebih bersih dan lebih berkelanjutan bagi masyarakat kita.

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