**Hypothesis 3 (H3).** *Environmental influences have a positive effect on sustainable consumption behavioural intention.*

In the framework of the European Union's sustainable policies, the promotion of sustainable development thinking has been a key issue. The promotion of the sustainability idea supports alternative consumption patterns; it increases consumers' knowledge and awareness connected with environmental and social problems, changes consumption and purchase behaviours, and enhances the acceptance level of sustainable consumption (Radziszewska 2019). In previous research, attention was paid to different contextual variables that have an impact on individuals' sustainable consumption behaviour, such as the price of green products, the availability of infrastructure, policy incentives (Wang et al. 2014), situation (Pimdee 2020), economic factors (Wang et al. 2019), etc. However, as far as we know, there are very few studies presenting empirical evidence of the effect of the SC construct on SCB. For instance, Sousa et al. (2022) confirm the existence of a positive relationship between companies' green communication and green purchase intentions. The findings of Piligrimiene et al. ˙ (2020) showed that the respondents had a positive attitude to green product promotion and to the application of other "engaging mechanisms" for sustainable consumption promotion. Therefore, it is hypothesised that:

**Hypothesis 4 (H4).** *SC promotion has a positive effect on sustainable consumption behavioural intention.*

## *2.3. Influence of Environmental Knowledge, Materialism, Environmental Influences, Promotion and Sustainable Consumption Behavioural Intention on Sustainable Consumption Behaviour*

Based on the theoretical background, we also decided to study the direct effect of the influencing factors selected by us on SCB. The same approach was adopted by other researchers as well (Saari et al. 2021; Wang et al. 2014; Brandão and Cupertino de Miranda 2022; Le 2020; Joshi and Rahman 2019; Nekmahmud et al. 2022). Most empirical results supported the conventional view that knowledge and behaviour are positively related (Wu et al. 2016). Figueroa-García et al. (2018) revealed that sustainable consumption behaviour was determined by environmental influences (in particular, the influence of family and friends, as well as that generated by cultural factors such as traditions). In conformity with other research, Matharu et al. (2021) concluded that sustainable consumption intention had a significant positive effect on sustainable consumption behaviour. In addressing this issue, the present study has presented the following five hypotheses:

**Hypothesis 5a (H5a).** *Environmental knowledge has a positive effect on sustainable consumption behaviour.*

**Hypothesis 5b (H5b).** *Materialism has a negative effect on sustainable consumption behaviour.*

**Hypothesis 5c (H5c).** *Environmental influences have a positive effect on sustainable consumption behaviour.*

**Hypothesis 5d (H5d).** *SC promotion has a positive effect on sustainable consumption behaviour.*

**Hypothesis 5e (H5e).** *Sustainable consumption behavioural intention has a positive effect on sustainable consumption behaviour.*

#### *2.4. The Mediating Effect of Sustainable Consumption Behavioural Intention*

As emphasised by Figueroa-García et al. (2018), it is important to not only evaluate the direct effect of one construct on another, but also the indirect effects produced by mediating constructs. This evaluation is performed by measuring the total effect, which is the sum of all direct and indirect effects. Because of the Theory of Planned Behaviour (TPB), which is one of the most influential theories among the studies on consumer behaviour, we considered examining the mediating role that behaviour intention has in the relationships between antecedents and SCB. In this study, we have referred sustainable consumption behavioural intention to people's willingness to act and consume more sustainably by making sacrifices or by paying more (Saari et al. 2021). Since the behavioural intention construct is often considered a mediator that facilitates some expected outcomes (e.g., attitude, subjective norms, perceived behavioural control), we have derived four mediation hypotheses:

**Hypothesis 6a (H6a).** *Sustainable consumption behavioural intention mediates the relationship between environmental knowledge and sustainable consumption behaviour.*

**Hypothesis 6b (H6b).** *Sustainable consumption behavioural intention mediates the relationship between materialism and sustainable consumption behaviour.*

**Hypothesis 6c (H6c).** *Sustainable consumption behavioural intention mediates the relationship between environmental influences and sustainable consumption behaviour.*

**Hypothesis 6d (H6d).** *Sustainable consumption behavioural intention mediates the relationship between SC promotion and sustainable consumption behaviour.*

#### *2.5. The Moderating Role of Age*

Scholars have argued that demographic variables, such as age, gender, income, etc., have a significant moderating influence on consumers' behaviour (Wu et al. 2016). As regards the effect of age on the occurrence of different SCB forms in particular, the results are contradictory. On the one hand, some studies found that, compared to younger customers, older customers tended to be more ecologically conscious (Han et al. 2009; Yahya et al. 2015). Accordingly, young consumers had a poor environmental attitude and low environmental concern and environmental knowledge (Dhir et al. 2021). Similarly, Witek and Ku ´zniar (2021) found that young people cared the least about being perceived as environmentally friendly. On the other hand, other studies explained that younger people were more environmentally concerned and made their decisions having considered the effect of their choice on the environment (Akehurst et al. 2012; Sheoran and Kumar 2022). As emphasised by Tripathi and Singh (2016), age could be an important variable while examining sustainable consumption, but inconsistencies of this kind in the previous literature need further research. Based on the above discussions, it is assumed that age can moderate all direct relationships developed in this study. Therefore, the following nine hypotheses have been postulated:

**Hypothesis 7a (H7a).** *Age moderates the relationship between environmental knowledge and sustainable consumption behavioural intention.*

**Hypothesis 7b (H7b).** *Age moderates the relationship between materialism and sustainable consumption behavioural intention.*

**Hypothesis 7c (H7c).** *Age moderates the relationship between environmental influences and sustainable consumption behavioural intention.*

**Hypothesis 7d (H7d).** *Age moderates the relationship between SC promotion and sustainable consumption behavioural intention.*

**Hypothesis 8a (H8a).** *Age moderates the relationship between environmental knowledge and sustainable consumption behaviour.*

**Hypothesis 8b (H8b).** *Age moderates the relationship between materialism and sustainable consumption behaviour.*

**Hypothesis 8c (H8c).** *Age moderates the relationship between environmental influences and sustainable consumption behaviour.*

**Hypothesis 8d (H8d).** *Age moderates the relationship between SC promotion and sustainable consumption behaviour.*

**Hypothesis 8e (H8e).** *Age moderates the relationship between sustainable consumption behavioural intention and sustainable consumption behaviour.*
